NAME
DBD::SQLite - Self-contained RDBMS in a DBI Driver
SYNOPSIS
use DBI;
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
DESCRIPTION
SQLite is a public domain file-based relational database engine
that you can find at <
http://www.sqlite.org/>.
DBD::SQLite is a Perl DBI driver for SQLite, that includes the
entire thing in the distribution. So in order to get a fast
transaction capable RDBMS working for your perl project you simply
have to install this module, and nothing else.
SQLite supports the following features:
Implements a large subset of SQL92
See <
http://www.sqlite.org/lang.html> for details.
A complete DB in a single disk file
Everything for your database is stored in a single disk file,
making it easier to move things around than with DBD::CSV.
Atomic commit and rollback
Yes, DBD::SQLite is small and light, but it supports full
transactions!
Extensible
User-defined aggregate or regular functions can be registered
with the SQL parser.
There's lots more to it, so please refer to the docs on the SQLite
web page, listed above, for SQL details. Also refer to DBI for
details on how to use DBI itself. The API works like every DBI
module does. However, currently many statement attributes are not
implemented or are limited by the typeless nature of the SQLite
database.
SQLITE VERSION
DBD::SQLite is usually compiled with a bundled SQLite library
(SQLite version 3.25.3 as of this release) for consistency.
However, a different version of SQLite may sometimes be used for
some reasons like security, or some new experimental features.
You can look at $DBD::SQLite::sqlite_version ("3.x.y" format) or
$DBD::SQLite::sqlite_version_number ("3xxxyyy" format) to find
which version of SQLite is actually used. You can also check
"DBD::SQLite::Constants::SQLITE_VERSION_NUMBER()".
You can also find how the library is compiled by calling
"DBD::SQLite::compile_options()" (see below).
NOTABLE DIFFERENCES FROM OTHER DRIVERS
Database Name Is A File Name
SQLite creates a file per a database. You should pass the "path"
of the database file (with or without a parent directory) in the
DBI connection string (as a database "name"):
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
The file is opened in read/write mode, and will be created if it
does not exist yet.
Although the database is stored in a single file, the directory
containing the database file must be writable by SQLite because
the library will create several temporary files there.
If the filename $dbfile is ":memory:", then a private, temporary
in-memory database is created for the connection. This in-memory
database will vanish when the database connection is closed. It is
handy for your library tests.
Note that future versions of SQLite might make use of additional
special filenames that begin with the ":" character. It is
recommended that when a database filename actually does begin with
a ":" character you should prefix the filename with a pathname
such as "./" to avoid ambiguity.
If the filename $dbfile is an empty string, then a private,
temporary on-disk database will be created. This private database
will be automatically deleted as soon as the database connection
is closed.
As of 1.41_01, you can pass URI filename (see
<
http://www.sqlite.org/uri.html>) as well for finer control:
my $dbh = DBI->connect("dbi:SQLite:uri=file:$path_to_dbfile?mode=rwc");
Note that this is not for remote SQLite database connection. You
can only connect to a local database.
Read-Only Database
You can set sqlite_open_flags (only) when you connect to a
database:
use DBD::SQLite::Constants qw/:file_open/;
my $dbh = DBI->connect("dbi:SQLite:$dbfile", undef, undef, {
sqlite_open_flags => SQLITE_OPEN_READONLY,
});
See <
http://www.sqlite.org/c3ref/open.html> for details.
As of 1.49_05, you can also make a database read-only by setting
"ReadOnly" attribute to true (only) when you connect to a
database. Actually you can set it after you connect, but in that
case, it can't make the database read-only, and you'll see a
warning (which you can hide by turning "PrintWarn" off).
DBD::SQLite And File::Temp
When you use File::Temp to create a temporary file/directory for
SQLite databases, you need to remember:
tempfile may be locked exclusively
You may want to use "tempfile()" to create a temporary
database filename for DBD::SQLite, but as noted in
File::Temp's POD, this file may have an exclusive lock under
some operating systems (notably Mac OSX), and result in a
"database is locked" error. To avoid this, set EXLOCK option
to false when you call tempfile().
($fh, $filename) = tempfile($template, EXLOCK => 0);
CLEANUP may not work unless a database is disconnected
When you set CLEANUP option to true when you create a
temporary directory with "tempdir()" or "newdir()", you may
have to disconnect databases explicitly before the temporary
directory is gone (notably under MS Windows).
(The above is quoted from the pod of File::Temp.)
If you don't need to keep or share a temporary database, use
":memory:" database instead. It's much handier and cleaner for
ordinary testing.
DBD::SQLite and fork()
Follow the advice in the SQLite FAQ
(<
https://sqlite.org/faq.html>).
Under Unix, you should not carry an open SQLite database
across a fork() system call into the child process. Problems
will result if you do.
You shouldn't (re)use a database handle you created (probably to
set up a database schema etc) before you fork(). Otherwise, you
might see a database corruption in the worst case.
If you need to fork(), (re)open a database after you fork(). You
might also want to tweak "sqlite_busy_timeout" and
"sqlite_use_immediate_transaction" (see below), depending on your
needs.
If you need a higher level of concurrency than SQLite supports,
consider using other client/server database engines.
Accessing A Database With Other Tools
To access the database from the command line, try using "dbish"
which comes with the DBI::Shell module. Just type:
dbish dbi:SQLite:foo.db
On the command line to access the file foo.db.
Alternatively you can install SQLite from the link above without
conflicting with DBD::SQLite and use the supplied "sqlite3"
command line tool.
Blobs
As of version 1.11, blobs should "just work" in SQLite as text
columns. However this will cause the data to be treated as a
string, so SQL statements such as length(x) will return the length
of the column as a NUL terminated string, rather than the size of
the blob in bytes. In order to store natively as a BLOB use the
following code:
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:dbfile","","");
my $blob = `cat foo.jpg`;
my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
$sth->bind_param(1, $blob, SQL_BLOB);
$sth->execute();
And then retrieval just works:
$sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
$sth->execute();
my $row = $sth->fetch;
my $blobo = $row->[1];
# now $blobo == $blob
Functions And Bind Parameters
As of this writing, a SQL that compares a return value of a
function with a numeric bind value like this doesn't work as you
might expect.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
This is because DBD::SQLite assumes that all the bind values are
text (and should be quoted) by default. Thus the above statement
becomes like this while executing:
SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";
There are three workarounds for this.
Use bind_param() explicitly
As shown above in the "BLOB" section, you can always use
"bind_param()" to tell the type of a bind value.
use DBI qw(:sql_types); # Don't forget this
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->bind_param(1, 5, SQL_INTEGER);
$sth->execute();
Add zero to make it a number
This is somewhat weird, but works anyway.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
});
$sth->execute(5);
Use SQL cast() function
This is more explicit way to do the above.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > cast(? as integer);
});
$sth->execute(5);
Set "sqlite_see_if_its_a_number" database handle attribute
As of version 1.32_02, you can use
"sqlite_see_if_its_a_number" to let DBD::SQLite to see if the
bind values are numbers or not.
$dbh->{sqlite_see_if_its_a_number} = 1;
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
You can set it to true when you connect to a database.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
This is the most straightforward solution, but as noted above,
existing data in your databases created by DBD::SQLite have
not always been stored as numbers, so this *might* cause other
obscure problems. Use this sparingly when you handle existing
databases. If you handle databases created by other tools like
native "sqlite3" command line tool, this attribute would help
you.
As of 1.41_04, "sqlite_see_if_its_a_number" works only for
bind values with no explicit type.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
my $sth = $dbh->prepare('INSERT INTO foo VALUES(?)');
# '1.230' will be inserted as a text, instead of 1.23 as a number,
# even though sqlite_see_if_its_a_number is set.
$sth->bind_param(1, '1.230', SQL_VARCHAR);
$sth->execute;
Placeholders
SQLite supports several placeholder expressions, including "?" and
":AAAA". Consult the DBI and SQLite documentation for details.
<
http://www.sqlite.org/lang_expr.html#varparam>
Note that a question mark actually means a next unused (numbered)
placeholder. You're advised not to use it with other (numbered or
named) placeholders to avoid confusion.
my $sth = $dbh->prepare(
'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
);
$sth->execute(1, 2);
Pragma
SQLite has a set of "Pragma"s to modify its operation or to query
for its internal data. These are specific to SQLite and are not
likely to work with other DBD libraries, but you may find some of
these are quite useful, including:
journal_mode
You can use this pragma to change the journal mode for SQLite
databases, maybe for better performance, or for compatibility.
Its default mode is "DELETE", which means SQLite uses a
rollback journal to implement transactions, and the journal is
deleted at the conclusion of each transaction. If you use
"TRUNCATE" instead of "DELETE", the journal will be truncated,
which is usually much faster.
A "WAL" (write-ahead log) mode is introduced as of SQLite
3.7.0. This mode is persistent, and it stays in effect even
after closing and reopening the database. In other words, once
the "WAL" mode is set in an application or in a test script,
the database becomes inaccessible by older clients. This tends
to be an issue when you use a system "sqlite3" executable
under a conservative operating system.
To fix this, You need to issue "PRAGMA journal_mode = DELETE"
(or "TRUNCATE") beforehand, or install a newer version of
"sqlite3".
legacy_file_format
If you happen to need to create a SQLite database that will
also be accessed by a very old SQLite client (prior to 3.3.0
released in Jan. 2006), you need to set this pragma to ON
before you create a database.
reverse_unordered_selects
You can set this pragma to ON to reverse the order of results
of SELECT statements without an ORDER BY clause so that you
can see if applications are making invalid assumptions about
the result order.
Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02)
enhanced its query optimizer and the order of results of a
SELECT statement without an ORDER BY clause may be different
from the one of the previous versions.
synchronous
You can set set this pragma to OFF to make some of the
operations in SQLite faster with a possible risk of database
corruption in the worst case. See also "Performance" section
below.
See <
http://www.sqlite.org/pragma.html> for more details.
Foreign Keys
SQLite has started supporting foreign key constraints since 3.6.19
(released on Oct 14, 2009; bundled in DBD::SQLite 1.26_05). To be
exact, SQLite has long been able to parse a schema with foreign
keys, but the constraints has not been enforced. Now you can issue
a "foreign_keys" pragma to enable this feature and enforce the
constraints, preferably as soon as you connect to a database and
you're not in a transaction:
$dbh->do("PRAGMA foreign_keys = ON");
And you can explicitly disable the feature whenever you like by
turning the pragma off:
$dbh->do("PRAGMA foreign_keys = OFF");
As of this writing, this feature is disabled by default by the
SQLite team, and by us, to secure backward compatibility, as this
feature may break your applications, and actually broke some for
us. If you have used a schema with foreign key constraints but
haven't cared them much and supposed they're always ignored for
SQLite, be prepared, and please do extensive testing to ensure
that your applications will continue to work when the foreign keys
support is enabled by default.
See <
http://www.sqlite.org/foreignkeys.html> for details.
Transactions
DBI/DBD::SQLite's transactions may be a bit confusing. They behave
differently according to the status of the "AutoCommit" flag:
When the AutoCommit flag is on
You're supposed to always use the auto-commit mode, except you
explicitly begin a transaction, and when the transaction
ended, you're supposed to go back to the auto-commit mode. To
begin a transaction, call "begin_work" method, or issue a
"BEGIN" statement. To end it, call "commit/rollback" methods,
or issue the corresponding statements.
$dbh->{AutoCommit} = 1;
$dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');
# $dbh->{AutoCommit} is turned off temporarily during a transaction;
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} is turned on again;
When the AutoCommit flag is off
You're supposed to always use the transactional mode, until
you explicitly turn on the AutoCommit flag. You can explicitly
issue a "BEGIN" statement (only when an actual transaction has
not begun yet) but you're not allowed to call "begin_work"
method (if you don't issue a "BEGIN", it will be issued
internally). You can commit or roll it back freely. Another
transaction will automatically begin if you execute another
statement.
$dbh->{AutoCommit} = 0;
# $dbh->do('BEGIN TRANSACTION') is not necessary, but possible
...
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} stays intact;
$dbh->{AutoCommit} = 1; # ends the transactional mode
This "AutoCommit" mode is independent from the autocommit mode of
the internal SQLite library, which always begins by a "BEGIN"
statement, and ends by a "COMMIT" or a <ROLLBACK>.
Transaction and Database Locking
The default transaction behavior of SQLite is "deferred", that
means, locks are not acquired until the first read or write
operation, and thus it is possible that another thread or process
could create a separate transaction and write to the database
after the "BEGIN" on the current thread has executed, and
eventually cause a "deadlock". To avoid this, DBD::SQLite
internally issues a "BEGIN IMMEDIATE" if you begin a transaction
by calling "begin_work" or by turning off "AutoCommit" (since
1.38_01).
If you really need to turn off this feature for some reasons, set
"sqlite_use_immediate_transaction" database handle attribute to
false, and the default "deferred" transaction will be used.
my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
sqlite_use_immediate_transaction => 0,
});
Or, issue a "BEGIN" statement explicitly each time you begin a
transaction.
See <
http://sqlite.org/lockingv3.html> for locking details.
"$sth->finish" and Transaction Rollback
As the DBI doc says, you almost certainly do not need to call
"finish" in DBI method if you fetch all rows (probably in a loop).
However, there are several exceptions to this rule, and
rolling-back of an unfinished "SELECT" statement is one of such
exceptional cases.
SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements in a
transaction (See <
http://sqlite.org/lang_transaction.html> for
details). So you need to call "finish" before you issue a
rollback.
$sth = $dbh->prepare("SELECT * FROM t");
$dbh->begin_work;
eval {
$sth->execute;
$row = $sth->fetch;
...
die "For some reason";
...
};
if($@) {
$sth->finish; # You need this for SQLite
$dbh->rollback;
} else {
$dbh->commit;
}
Processing Multiple Statements At A Time
DBI's statement handle is not supposed to process multiple
statements at a time. So if you pass a string that contains
multiple statements (a "dump") to a statement handle (via
"prepare" or "do"), DBD::SQLite only processes the first
statement, and discards the rest.
If you need to process multiple statements at a time, set a
"sqlite_allow_multiple_statements" attribute of a database handle
to true when you connect to a database, and "do" method takes care
of the rest (since 1.30_01, and without creating DBI's statement
handles internally since 1.47_01). If you do need to use "prepare"
or "prepare_cached" (which I don't recommend in this case, because
typically there's no placeholder nor reusable part in a dump), you
can look at << $sth->{sqlite_unprepared_statements} >> to retrieve
what's left, though it usually contains nothing but white spaces.
TYPE statement attribute
Because of historical reasons, DBD::SQLite's "TYPE" statement
handle attribute returns an array ref of string values, contrary
to the DBI specification. This value is also less useful for
SQLite users because SQLite uses dynamic type system (that means,
the datatype of a value is associated with the value itself, not
with its container).
Performance
SQLite is fast, very fast. Matt processed his 72MB log file with
it, inserting the data (400,000+ rows) by using transactions and
only committing every 1000 rows (otherwise the insertion is quite
slow), and then performing queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to
return, but what surprised him most of all was:
SELECT url, count(*) as count
FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20
To discover the top 20 hit URLs on the site (<
http://axkit.org>),
and it returned within 2 seconds. He was seriously considering
switching his log analysis code to use this little speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz
PIII.
For best performance be sure to tune your hdparm settings if you
are using linux. Also you might want to set:
PRAGMA synchronous = OFF
Which will prevent SQLite from doing fsync's when writing (which
slows down non-transactional writes significantly) at the expense
of some peace of mind. Also try playing with the cache_size
pragma.
The memory usage of SQLite can also be tuned using the cache_size
pragma.
$dbh->do("PRAGMA cache_size = 800000");
The above will allocate 800M for DB cache; the default is 2M. Your
sweet spot probably lies somewhere in between.
DRIVER PRIVATE ATTRIBUTES
Database Handle Attributes
sqlite_version
Returns the version of the SQLite library which DBD::SQLite is
using, e.g., "2.8.0". Can only be read.
sqlite_unicode
If set to a true value, DBD::SQLite will turn the UTF-8 flag
on for all text strings coming out of the database (this
feature is currently disabled for perl < 5.8.5). For more
details on the UTF-8 flag see perlunicode. The default is for
the UTF-8 flag to be turned off.
Also note that due to some bizarreness in SQLite's type system
(see <
http://www.sqlite.org/datatype3.html>), if you want to
retain blob-style behavior for some columns under
"$dbh->{sqlite_unicode} = 1" (say, to store images in the
database), you have to state so explicitly using the
3-argument form of "bind_param" in DBI when doing updates:
use DBI qw(:sql_types);
$dbh->{sqlite_unicode} = 1;
my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");
# Binary_data will be stored as is.
$sth->bind_param(1, $binary_data, SQL_BLOB);
Defining the column type as "BLOB" in the DDL is not
sufficient.
This attribute was originally named as "unicode", and renamed
to "sqlite_unicode" for integrity since version 1.26_06. Old
"unicode" attribute is still accessible but will be deprecated
in the near future.
sqlite_allow_multiple_statements
If you set this to true, "do" method will process multiple
statements at one go. This may be handy, but with performance
penalty. See above for details.
sqlite_use_immediate_transaction
If you set this to true, DBD::SQLite tries to issue a "begin
immediate transaction" (instead of "begin transaction") when
necessary. See above for details.
As of version 1.38_01, this attribute is set to true by
default. If you really need to use "deferred" transactions for
some reasons, set this to false explicitly.
sqlite_see_if_its_a_number
If you set this to true, DBD::SQLite tries to see if the bind
values are number or not, and does not quote if they are
numbers. See above for details.
sqlite_extended_result_codes
If set to true, DBD::SQLite uses extended result codes where
appropriate (see <
http://www.sqlite.org/rescode.html>).
Statement Handle Attributes
sqlite_unprepared_statements
Returns an unprepared part of the statement you pass to
"prepare". Typically this contains nothing but white spaces
after a semicolon. See above for details.
METHODS
See also to the DBI documentation for the details of other common
methods.
table_info
$sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);
Returns all tables and schemas (databases) as specified in
"table_info" in DBI. The schema and table arguments will do a
"LIKE" search. You can specify an ESCAPE character by including an
'Escape' attribute in \%attr. The $type argument accepts a comma
separated list of the following types 'TABLE', 'VIEW', 'LOCAL
TEMPORARY' and 'SYSTEM TABLE' (by default all are returned). Note
that a statement handle is returned, and not a direct list of
tables.
The following fields are returned:
TABLE_CAT: Always NULL, as SQLite does not have the concept of
catalogs.
TABLE_SCHEM: The name of the schema (database) that the table or
view is in. The default schema is 'main', temporary tables are in
'temp' and other databases will be in the name given when the
database was attached.
TABLE_NAME: The name of the table or view.
TABLE_TYPE: The type of object returned. Will be one of 'TABLE',
'VIEW', 'LOCAL TEMPORARY' or 'SYSTEM TABLE'.
primary_key, primary_key_info
@names = $dbh->primary_key(undef, $schema, $table);
$sth = $dbh->primary_key_info(undef, $schema, $table, \%attr);
You can retrieve primary key names or more detailed information.
As noted above, SQLite does not have the concept of catalogs, so
the first argument of the methods is usually "undef", and you'll
usually set "undef" for the second one (unless you want to know
the primary keys of temporary tables).
foreign_key_info
$sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
undef, $fk_schema, $fk_table);
Returns information about foreign key constraints, as specified in
"foreign_key_info" in DBI, but with some limitations :
* information in rows returned by the $sth is incomplete with
respect to the "foreign_key_info" in DBI specification. All
requested fields are present, but the content is "undef" for
some of them.
The following nonempty fields are returned :
PKTABLE_NAME: The primary (unique) key table identifier.
PKCOLUMN_NAME: The primary (unique) key column identifier.
FKTABLE_NAME: The foreign key table identifier.
FKCOLUMN_NAME: The foreign key column identifier.
KEY_SEQ: The column sequence number (starting with 1), when
several columns belong to a same constraint.
UPDATE_RULE: The referential action for the UPDATE rule. The
following codes are defined:
CASCADE 0
RESTRICT 1
SET NULL 2
NO ACTION 3
SET DEFAULT 4
Default is 3 ('NO ACTION').
DELETE_RULE: The referential action for the DELETE rule. The codes
are the same as for UPDATE_RULE.
DEFERRABILITY: The following codes are defined:
INITIALLY DEFERRED 5
INITIALLY IMMEDIATE 6
NOT DEFERRABLE 7
UNIQUE_OR_PRIMARY: Whether the column is primary or unique.
Note: foreign key support in SQLite must be explicitly turned on
through a "PRAGMA" command; see "Foreign keys" earlier in this
manual.
statistics_info
$sth = $dbh->statistics_info(undef, $schema, $table,
$unique_only, $quick);
Returns information about a table and it's indexes, as specified
in "statistics_info" in DBI, but with some limitations :
* information in rows returned by the $sth is incomplete with
respect to the "statistics_info" in DBI specification. All
requested fields are present, but the content is "undef" for
some of them.
The following nonempty fields are returned :
TABLE_SCHEM: The name of the schema (database) that the table is
in. The default schema is 'main', temporary tables are in 'temp'
and other databases will be in the name given when the database
was attached.
TABLE_NAME: The name of the table
NON_UNIQUE: Contains 0 for unique indexes, 1 for non-unique
indexes
INDEX_NAME: The name of the index
TYPE: SQLite uses 'btree' for all it's indexes
ORDINAL_POSITION: Column sequence number (starting with 1).
COLUMN_NAME: The name of the column
ping
my $bool = $dbh->ping;
returns true if the database file exists (or the database is
in-memory), and the database connection is active.
DRIVER PRIVATE METHODS
The following methods can be called via the func() method with a
little tweak, but the use of func() method is now discouraged by
the DBI author for various reasons (see DBI's document
<
https://metacpan.org/pod/DBI::DBD#Using-install_method()-to-expos
e-driver-private-methods> for details). So, if you're using DBI >=
1.608, use these "sqlite_" methods. If you need to use an older
DBI, you can call these like this:
$dbh->func( ..., "(method name without sqlite_ prefix)" );
Exception: "sqlite_trace" should always be called as is, even with
"func()" method (to avoid conflict with DBI's trace() method).
$dbh->func( ..., "sqlite_trace");
$dbh->sqlite_last_insert_rowid()
This method returns the last inserted rowid. If you specify an
INTEGER PRIMARY KEY as the first column in your table, that is the
column that is returned. Otherwise, it is the hidden ROWID column.
See the SQLite docs for details.
Generally you should not be using this method. Use the DBI
last_insert_id method instead. The usage of this is:
$h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])
Running "$h->last_insert_id("","","","")" is the equivalent of
running "$dbh->sqlite_last_insert_rowid()" directly.
$dbh->sqlite_db_filename()
Retrieve the current (main) database filename. If the database is
in-memory or temporary, this returns "undef".
$dbh->sqlite_busy_timeout()
Retrieve the current busy timeout.
$dbh->sqlite_busy_timeout( $ms )
Set the current busy timeout. The timeout is in milliseconds.
$dbh->sqlite_create_function( $name, $argc, $code_ref, $flags )
This method will register a new function which will be usable in
an SQL query. The method's parameters are:
$name
The name of the function. This is the name of the function as
it will be used from SQL.
$argc
The number of arguments taken by the function. If this number
is -1, the function can take any number of arguments.
$code_ref
This should be a reference to the function's implementation.
$flags
You can optionally pass an extra flag bit to create_function,
which then would be ORed with SQLITE_UTF8 (default). As of
1.47_02 (SQLite 3.8.9), only meaning bit is
SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can
make the function perform better. See C API documentation at
<
http://sqlite.org/c3ref/create_function.html> for details.
For example, here is how to define a now() function which returns
the current number of seconds since the epoch:
$dbh->sqlite_create_function( 'now', 0, sub { return time } );
After this, it could be used from SQL as:
INSERT INTO mytable ( now() );
REGEXP function
SQLite includes syntactic support for an infix operator 'REGEXP',
but without any implementation. The "DBD::SQLite" driver
automatically registers an implementation that performs standard
perl regular expression matching, using current locale. So for
example you can search for words starting with an 'A' with a query
like
SELECT * from table WHERE column REGEXP '\bA\w+'
If you want case-insensitive searching, use perl regex flags, like
this :
SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'
The default REGEXP implementation can be overridden through the
"create_function" API described above.
Note that regexp matching will not use SQLite indices, but will
iterate over all rows, so it could be quite costly in terms of
performance.
$dbh->sqlite_create_collation( $name, $code_ref )
This method manually registers a new function which will be usable
in an SQL query as a COLLATE option for sorting. Such functions
can also be registered automatically on demand: see section
"COLLATION FUNCTIONS" below.
The method's parameters are:
$name
The name of the function exposed to SQL.
$code_ref
Reference to the function's implementation. The driver will
check that this is a proper sorting function.
$dbh->sqlite_collation_needed( $code_ref )
This method manually registers a callback function that will be
invoked whenever an undefined collation sequence is required from
an SQL statement. The callback is invoked as
$code_ref->($dbh, $collation_name)
and should register the desired collation using
"sqlite_create_collation".
An initial callback is already registered by "DBD::SQLite", so for
most common cases it will be simpler to just add your collation
sequences in the %DBD::SQLite::COLLATION hash (see section
"COLLATION FUNCTIONS" below).
$dbh->sqlite_create_aggregate( $name, $argc, $pkg, $flags )
This method will register a new aggregate function which can then
be used from SQL. The method's parameters are:
$name
The name of the aggregate function, this is the name under
which the function will be available from SQL.
$argc
This is an integer which tells the SQL parser how many
arguments the function takes. If that number is -1, the
function can take any number of arguments.
$pkg
This is the package which implements the aggregator interface.
$flags
You can optionally pass an extra flag bit to create_aggregate,
which then would be ORed with SQLITE_UTF8 (default). As of
1.47_02 (SQLite 3.8.9), only meaning bit is
SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can
make the function perform better. See C API documentation at
<
http://sqlite.org/c3ref/create_function.html> for details.
The aggregator interface consists of defining three methods:
new()
This method will be called once to create an object which
should be used to aggregate the rows in a particular group.
The step() and finalize() methods will be called upon the
reference return by the method.
step(@_)
This method will be called once for each row in the aggregate.
finalize()
This method will be called once all rows in the aggregate were
processed and it should return the aggregate function's
result. When there is no rows in the aggregate, finalize()
will be called right after new().
Here is a simple aggregate function which returns the variance
(example adapted from pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($v - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->sqlite_create_aggregate( "variance", 1, 'variance' );
The aggregate function can then be used as:
SELECT group_name, variance(score)
FROM results
GROUP BY group_name;
For more examples, see the DBD::SQLite::Cookbook.
$dbh->sqlite_progress_handler( $n_opcodes, $code_ref )
This method registers a handler to be invoked periodically during
long running calls to SQLite.
An example use for this interface is to keep a GUI updated during
a large query. The parameters are:
$n_opcodes
The progress handler is invoked once for every $n_opcodes
virtual machine opcodes in SQLite.
$code_ref
Reference to the handler subroutine. If the progress handler
returns non-zero, the SQLite operation is interrupted. This
feature can be used to implement a "Cancel" button on a GUI
dialog box.
Set this argument to "undef" if you want to unregister a
previous progress handler.
$dbh->sqlite_commit_hook( $code_ref )
This method registers a callback function to be invoked whenever a
transaction is committed. Any callback set by a previous call to
"sqlite_commit_hook" is overridden. A reference to the previous
callback (if any) is returned. Registering an "undef" disables the
callback.
When the commit hook callback returns zero, the commit operation
is allowed to continue normally. If the callback returns non-zero,
then the commit is converted into a rollback (in that case, any
attempt to *explicitly* call "$dbh->rollback()" afterwards would
yield an error).
$dbh->sqlite_rollback_hook( $code_ref )
This method registers a callback function to be invoked whenever a
transaction is rolled back. Any callback set by a previous call to
"sqlite_rollback_hook" is overridden. A reference to the previous
callback (if any) is returned. Registering an "undef" disables the
callback.
$dbh->sqlite_update_hook( $code_ref )
This method registers a callback function to be invoked whenever a
row is updated, inserted or deleted. Any callback set by a
previous call to "sqlite_update_hook" is overridden. A reference
to the previous callback (if any) is returned. Registering an
"undef" disables the callback.
The callback will be called as
$code_ref->($action_code, $database, $table, $rowid)
where
$action_code
is an integer equal to either "DBD::SQLite::INSERT",
"DBD::SQLite::DELETE" or "DBD::SQLite::UPDATE" (see "Action
Codes");
$database
is the name of the database containing the affected row;
$table
is the name of the table containing the affected row;
$rowid
is the unique 64-bit signed integer key of the affected row
within that table.
$dbh->sqlite_set_authorizer( $code_ref )
This method registers an authorizer callback to be invoked
whenever SQL statements are being compiled by the "prepare" in DBI
method. The authorizer callback should return "DBD::SQLite::OK" to
allow the action, "DBD::SQLite::IGNORE" to disallow the specific
action but allow the SQL statement to continue to be compiled, or
"DBD::SQLite::DENY" to cause the entire SQL statement to be
rejected with an error. If the authorizer callback returns any
other value, then "prepare" call that triggered the authorizer
will fail with an error message.
An authorizer is used when preparing SQL statements from an
untrusted source, to ensure that the SQL statements do not try to
access data they are not allowed to see, or that they do not try
to execute malicious statements that damage the database. For
example, an application may allow a user to enter arbitrary SQL
queries for evaluation by a database. But the application does not
want the user to be able to make arbitrary changes to the
database. An authorizer could then be put in place while the
user-entered SQL is being prepared that disallows everything
except SELECT statements.
The callback will be called as
$code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)
where
$action_code
is an integer that specifies what action is being authorized
(see "Action Codes").
$string1, $string2
are strings that depend on the action code (see "Action
Codes").
$database
is the name of the database ("main", "temp", etc.) if
applicable.
$trigger_or_view
is the name of the inner-most trigger or view that is
responsible for the access attempt, or "undef" if this access
attempt is directly from top-level SQL code.
$dbh->sqlite_backup_from_file( $filename )
This method accesses the SQLite Online Backup API, and will take a
backup of the named database file, copying it to, and overwriting,
your current database connection. This can be particularly handy
if your current connection is to the special :memory: database,
and you wish to populate it from an existing DB.
$dbh->sqlite_backup_to_file( $filename )
This method accesses the SQLite Online Backup API, and will take a
backup of the currently connected database, and write it out to
the named file.
$dbh->sqlite_enable_load_extension( $bool )
Calling this method with a true value enables loading (external)
SQLite3 extensions. After the call, you can load extensions like
this:
$dbh->sqlite_enable_load_extension(1);
$sth = $dbh->prepare("select load_extension('libsqlitefunctions.so')")
or die "Cannot prepare: " . $dbh->errstr();
$dbh->sqlite_load_extension( $file, $proc )
Loading an extension by a select statement (with the
"load_extension" SQLite3 function like above) has some
limitations. If you need to, say, create other functions from an
extension, use this method. $file (a path to the extension) is
mandatory, and $proc (an entry point name) is optional. You need
to call "sqlite_enable_load_extension" before calling
"sqlite_load_extension".
$dbh->sqlite_trace( $code_ref )
This method registers a trace callback to be invoked whenever SQL
statements are being run.
The callback will be called as
$code_ref->($statement)
where
$statement
is a UTF-8 rendering of the SQL statement text as the
statement first begins executing.
Additional callbacks might occur as each triggered subprogram is
entered. The callbacks for triggers contain a UTF-8 SQL comment
that identifies the trigger.
See also "TRACING" in DBI for better tracing options.
$dbh->sqlite_profile( $code_ref )
This method registers a profile callback to be invoked whenever a
SQL statement finishes.
The callback will be called as
$code_ref->($statement, $elapsed_time)
where
$statement
is the original statement text (without bind parameters).
$elapsed_time
is an estimate of wall-clock time of how long that statement
took to run (in milliseconds).
This method is considered experimental and is subject to change in
future versions of SQLite.
See also DBI::Profile for better profiling options.
$dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )
is for internal use only.
$dbh->sqlite_db_status()
Returns a hash reference that holds a set of status information of
database connection such as cache usage. See
<
http://www.sqlite.org/c3ref/c_dbstatus_options.html> for details.
You may also pass 0 as an argument to reset the status.
$sth->sqlite_st_status()
Returns a hash reference that holds a set of status information of
SQLite statement handle such as full table scan count. See
<
http://www.sqlite.org/c3ref/c_stmtstatus_counter.html> for
details. Statement status only holds the current value.
my $status = $sth->sqlite_st_status();
my $cur = $status->{fullscan_step};
You may also pass 0 as an argument to reset the status.
$dbh->sqlite_create_module()
Registers a name for a *virtual table module*. Module names must
be registered before creating a new virtual table using the module
and before using a preexisting virtual table for the module.
Virtual tables are explained in DBD::SQLite::VirtualTable.
$dbh->sqlite_limit( $category_id, $new_value )
Sets a new run-time limit for the category, and returns the
current limit. If the new value is a negative number (or omitted),
the limit is unchanged and just returns the current limit.
Category ids (SQLITE_LIMIT_LENGTH, SQLITE_LIMIT_VARIABLE_NUMBER,
etc) can be imported from DBD::SQLite::Constants.
DRIVER FUNCTIONS
DBD::SQLite::compile_options()
Returns an array of compile options (available since SQLite
3.6.23, bundled in DBD::SQLite 1.30_01), or an empty array if the
bundled library is old or compiled with
SQLITE_OMIT_COMPILEOPTION_DIAGS.
DBD::SQLite::sqlite_status()
Returns a hash reference that holds a set of status information of
SQLite runtime such as memory usage or page cache usage (see
<
http://www.sqlite.org/c3ref/c_status_malloc_count.html> for
details). Each of the entry contains the current value and the
highwater value.
my $status = DBD::SQLite::sqlite_status();
my $cur = $status->{memory_used}{current};
my $high = $status->{memory_used}{highwater};
You may also pass 0 as an argument to reset the status.
DBD::SQLite::strlike($pattern, $string, $escape_char), DBD::SQLite::strglob($pattern, $string)
As of 1.49_05 (SQLite 3.10.0), you can use these two functions to
see if a string matches a pattern. These may be useful when you
create a virtual table or a custom function. See
<
http://sqlite.org/c3ref/strlike.html> and
<
http://sqlite.org/c3ref/strglob.html> for details.
DRIVER CONSTANTS
A subset of SQLite C constants are made available to Perl, because
they may be needed when writing hooks or authorizer callbacks. For
accessing such constants, the "DBD::SQLite" module must be
explicitly "use"d at compile time. For example, an authorizer that
forbids any DELETE operation would be written as follows :
use DBD::SQLite;
$dbh->sqlite_set_authorizer(sub {
my $action_code = shift;
return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
: DBD::SQLite::OK;
});
The list of constants implemented in "DBD::SQLite" is given below;
more information can be found ad at
<
http://www.sqlite.org/c3ref/constlist.html>.
Authorizer Return Codes
OK
DENY
IGNORE
Action Codes
The "set_authorizer" method registers a callback function that is
invoked to authorize certain SQL statement actions. The first
parameter to the callback is an integer code that specifies what
action is being authorized. The second and third parameters to the
callback are strings, the meaning of which varies according to the
action code. Below is the list of action codes, together with
their associated strings.
# constant string1 string2
# ======== ======= =======
CREATE_INDEX Index Name Table Name
CREATE_TABLE Table Name undef
CREATE_TEMP_INDEX Index Name Table Name
CREATE_TEMP_TABLE Table Name undef
CREATE_TEMP_TRIGGER Trigger Name Table Name
CREATE_TEMP_VIEW View Name undef
CREATE_TRIGGER Trigger Name Table Name
CREATE_VIEW View Name undef
DELETE Table Name undef
DROP_INDEX Index Name Table Name
DROP_TABLE Table Name undef
DROP_TEMP_INDEX Index Name Table Name
DROP_TEMP_TABLE Table Name undef
DROP_TEMP_TRIGGER Trigger Name Table Name
DROP_TEMP_VIEW View Name undef
DROP_TRIGGER Trigger Name Table Name
DROP_VIEW View Name undef
INSERT Table Name undef
PRAGMA Pragma Name 1st arg or undef
READ Table Name Column Name
SELECT undef undef
TRANSACTION Operation undef
UPDATE Table Name Column Name
ATTACH Filename undef
DETACH Database Name undef
ALTER_TABLE Database Name Table Name
REINDEX Index Name undef
ANALYZE Table Name undef
CREATE_VTABLE Table Name Module Name
DROP_VTABLE Table Name Module Name
FUNCTION undef Function Name
SAVEPOINT Operation Savepoint Name
COLLATION FUNCTIONS
Definition
SQLite v3 provides the ability for users to supply arbitrary
comparison functions, known as user-defined "collation sequences"
or "collating functions", to be used for comparing two text
values. <
http://www.sqlite.org/datatype3.html#collation> explains
how collations are used in various SQL expressions.
Builtin collation sequences
The following collation sequences are builtin within SQLite :
BINARY
Compares string data using memcmp(), regardless of text
encoding.
NOCASE
The same as binary, except the 26 upper case characters of
ASCII are folded to their lower case equivalents before the
comparison is performed. Note that only ASCII characters are
case folded. SQLite does not attempt to do full UTF case
folding due to the size of the tables required.
RTRIM
The same as binary, except that trailing space characters are
ignored.
In addition, "DBD::SQLite" automatically installs the following
collation sequences :
perl
corresponds to the Perl "cmp" operator
perllocale
Perl "cmp" operator, in a context where "use locale" is
activated.
Usage
You can write for example
CREATE TABLE foo(
txt1 COLLATE perl,
txt2 COLLATE perllocale,
txt3 COLLATE nocase
)
or
SELECT * FROM foo ORDER BY name COLLATE perllocale
Unicode handling
If the attribute "$dbh->{sqlite_unicode}" is set, strings coming
from the database and passed to the collation function will be
properly tagged with the utf8 flag; but this only works if the
"sqlite_unicode" attribute is set before the first call to a perl
collation sequence . The recommended way to activate unicode is to
set the parameter at connection time :
my $dbh = DBI->connect(
"dbi:SQLite:dbname=foo", "", "",
{
RaiseError => 1,
sqlite_unicode => 1,
}
);
Adding user-defined collations
The native SQLite API for adding user-defined collations is
exposed through methods "sqlite_create_collation" and
"sqlite_collation_needed".
To avoid calling these functions every time a $dbh handle is
created, "DBD::SQLite" offers a simpler interface through the
%DBD::SQLite::COLLATION hash : just insert your own collation
functions in that hash, and whenever an unknown collation name is
encountered in SQL, the appropriate collation function will be
loaded on demand from the hash. For example, here is a way to sort
text values regardless of their accented characters :
use DBD::SQLite;
$DBD::SQLite::COLLATION{no_accents} = sub {
my ( $a, $b ) = map lc, @_;
tr[��������������������������
[aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
$a cmp $b;
};
my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile");
my $sql = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
my $rows = $dbh->selectall_arrayref($sql);
The builtin "perl" or "perllocale" collations are predefined in
that same hash.
The COLLATION hash is a global registry within the current
process; hence there is a risk of undesired side-effects.
Therefore, to prevent action at distance, the hash is implemented
as a "write-only" hash, that will happily accept new entries, but
will raise an exception if any attempt is made to override or
delete a existing entry (including the builtin "perl" and
"perllocale").
If you really, really need to change or delete an entry, you can
always grab the tied object underneath %DBD::SQLite::COLLATION ---
but don't do that unless you really know what you are doing. Also
observe that changes in the global hash will not modify existing
collations in existing database handles: it will only affect new
*requests* for collations. In other words, if you want to change
the behaviour of a collation within an existing $dbh, you need to
call the "create_collation" method directly.
FULLTEXT SEARCH
SQLite is bundled with an extension module for full-text indexing.
Tables with this feature enabled can be efficiently queried to
find rows that contain one or more instances of some specified
words, in any column, even if the table contains many large
documents.
Explanations for using this feature are provided in a separate
document: see DBD::SQLite::Fulltext_search.
R* TREE SUPPORT
The RTREE extension module within SQLite adds support for creating
a R-Tree, a special index for range and multidimensional queries.
This allows users to create tables that can be loaded with (as an
example) geospatial data such as latitude/longitude coordinates
for buildings within a city :
CREATE VIRTUAL TABLE city_buildings USING rtree(
id, -- Integer primary key
minLong, maxLong, -- Minimum and maximum longitude
minLat, maxLat -- Minimum and maximum latitude
);
then query which buildings overlap or are contained within a
specified region:
# IDs that are contained within query coordinates
my $contained_sql = <<"";
SELECT id FROM city_buildings
WHERE minLong >= ? AND maxLong <= ?
AND minLat >= ? AND maxLat <= ?
# ... and those that overlap query coordinates
my $overlap_sql = <<"";
SELECT id FROM city_buildings
WHERE maxLong >= ? AND minLong <= ?
AND maxLat >= ? AND minLat <= ?
my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
For more detail, please see the SQLite R-Tree page
(<
http://www.sqlite.org/rtree.html>). Note that custom R-Tree
queries using callbacks, as mentioned in the prior link, have not
been implemented yet.
VIRTUAL TABLES IMPLEMENTED IN PERL
SQLite has a concept of "virtual tables" which look like regular
tables but are implemented internally through specific functions.
The fulltext or R* tree features described in the previous
chapters are examples of such virtual tables, implemented in C
code.
"DBD::SQLite" also supports virtual tables implemented in *Perl
code*: see DBD::SQLite::VirtualTable for using or implementing
such virtual tables. These can have many interesting uses for
joining regular DBMS data with some other kind of data within your
Perl programs. Bundled with the present distribution are :
* DBD::SQLite::VirtualTable::FileContent : implements a virtual
column that exposes file contents. This is especially useful
in conjunction with a fulltext index; see
DBD::SQLite::Fulltext_search.
* DBD::SQLite::VirtualTable::PerlData : binds to a Perl array
within the Perl program. This can be used for simple
import/export operations, for debugging purposes, for joining
data from different sources, etc.
Other Perl virtual tables may also be published separately on
CPAN.
FOR DBD::SQLITE EXTENSION AUTHORS
Since 1.30_01, you can retrieve the bundled SQLite C source and/or
header like this:
use File::ShareDir 'dist_dir';
use File::Spec::Functions 'catfile';
# the whole sqlite3.h header
my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');
# or only a particular header, amalgamated in sqlite3.c
my $what_i_want = 'parse.h';
my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
open my $fh, '<', $sqlite3_c or die $!;
my $code = do { local $/; <$fh> };
my ($parse_h) = $code =~ m{(
/\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
.+?
/\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
)}sx;
open my $out, '>', $what_i_want or die $!;
print $out $parse_h;
close $out;
You usually want to use this in your extension's "Makefile.PL",
and you may want to add DBD::SQLite to your extension's
"CONFIGURE_REQUIRES" to ensure your extension users use the same C
source/header they use to build DBD::SQLite itself (instead of the
ones installed in their system).
TO DO
The following items remain to be done.
Leak Detection
Implement one or more leak detection tests that only run during
AUTOMATED_TESTING and RELEASE_TESTING and validate that none of
the C code we work with leaks.
Stream API for Blobs
Reading/writing into blobs using "sqlite2_blob_open" /
"sqlite2_blob_close".
Support for custom callbacks for R-Tree queries
Custom queries of a R-Tree index using a callback are possible
with the SQLite C API (<
http://www.sqlite.org/rtree.html>), so one
could potentially use a callback that narrowed the result set down
based on a specific need, such as querying for overlapping
circles.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<
http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>
Note that bugs of bundled SQLite library (i.e. bugs in
"sqlite3.[ch]") should be reported to the SQLite developers at
sqlite.org via their bug tracker or via their mailing list.
The master repository is on GitHub:
<
https://github.com/DBD-SQLite/DBD-SQLite>.
We also have a mailing list:
<
http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbd-sqlite>
AUTHORS
Matt Sergeant <
[email protected]>
Francis J. Lacoste <
[email protected]>
Wolfgang Sourdeau <
[email protected]>
Adam Kennedy <
[email protected]>
Max Maischein <
[email protected]>
Laurent Dami <
[email protected]>
Kenichi Ishigaki <
[email protected]>
COPYRIGHT
The bundled SQLite code in this distribution is Public Domain.
DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.
Some parts copyright 2008 Francis J. Lacoste.
Some parts copyright 2008 Wolfgang Sourdeau.
Some parts copyright 2008 - 2013 Adam Kennedy.
Some parts copyright 2009 - 2013 Kenichi Ishigaki.
Some parts derived from DBD::SQLite::Amalgamation copyright 2008
Audrey Tang.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file
included with this module.
