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.
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.
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);
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.
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);
Foreign Keys
BE PREPARED! WOLVES APPROACH!!
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 pragma actually
to enable this feature and enforce the constraints.
To do this, issue the following pragma (see below), 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. It is very
likely that the sqlite team will turn it default-on in the future, and
we plan to do it NO LATER THAN they do so.
See <
http://www.sqlite.org/foreignkeys.html> for details.
Pragma
SQLite has a set of "Pragma"s to modifiy 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. DBD::SQLite actually sets some (like "show_datatypes") for you
when you connect to a database. See <
http://www.sqlite.org/pragma.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
Transaction by "AutoCommit" or "begin_work" is nice and handy, but
sometimes you may get an annoying "database is locked" error. This
typically happens when someone begins a transaction, and tries to write
to a database while other person is reading from the database (in
another transaction). You might be surprised but SQLite doesn't lock a
database when you just begin a normal (deferred) transaction to maximize
concurrency. It reserves a lock when you issue a statement to write, but
until you actually try to write with a "commit" statement, it allows
other people to read from the database. However, reading from the
database also requires "shared lock", and that prevents to give you the
"exclusive lock" you reserved, thus you get the "database is locked"
error, and other people will get the same error if they try to write
afterwards, as you still have a "pending" lock. "busy_timeout" doesn't
help in this case.
To avoid this, set a transaction type explicitly. You can issue a "begin
immediate transaction" (or "begin exclusive transaction") for each
transaction, or set "sqlite_use_immediate_transaction" database handle
attribute to true (since 1.30_02) to always use an immediate transaction
(even when you simply use "begin_work" or turn off the "AutoCommit".).
my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
sqlite_use_immediate_transaction => 1,
});
Note that this works only when all of the connections use the same
(non-deferred) transaction. See <
http://sqlite.org/lockingv3.html> for
locking details.
"$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 {
$dbh->commit;
}
Processing Multiple Statements At A Time
DBI's statement handle is not supposed to process multiple statements at
a time. So if you pass a string that contains multiple statements (a
"dump") to a statement handle (via "prepare" or "do"), DBD::SQLite only
processes the first statement, and discards the rest.
Since 1.30_01, you can retrieve those ignored (unprepared) statements
via "$sth->{sqlite_unprepared_statements}". It usually contains nothing
but white spaces, but if you really care, you can check this attribute
to see if there's anything left undone. Also, if you set a
"sqlite_allow_multiple_statements" attribute of a database handle to
true when you connect to a database, "do" method automatically checks
the "sqlite_unprepared_statements" attribute, and if it finds anything
undone (even if what's left is just a single white space), it repeats
the process again, to the end.
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.
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.
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 mothods is usually "undef", and you'll usually set
"undef" for the second one (unless you want to know the primary keys of
temporary tables).
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
<
http://search.cpan.org/dist/DBI/lib/DBI/DBD.pm#Using_install_method()_t
o_expose_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_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 )
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.
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 use 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 )
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.
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 ) {
$sigma += ($x - $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 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_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.
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.
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
The FTS3 extension module within SQLite allows users to create special
tables with a built-in full-text index (hereafter "FTS3 tables"). The
full-text index allows the user to efficiently query the database for
all rows that contain one or more instances of a specified word
(hereafter a "token"), even if the table contains many large documents.
Short introduction to FTS3
The detailed documentation for FTS3 can be found at
<
http://www.sqlite.org/fts3.html>. Here is a very short example :
$dbh->do(<<"") or die DBI::errstr;
CREATE VIRTUAL TABLE fts_example USING fts3(content)
my $sth = $dbh->prepare("INSERT INTO fts_example(content) VALUES (?))");
$sth->execute($_) foreach @docs_to_insert;
my $results = $dbh->selectall_arrayref(<<"");
SELECT docid, snippet(content) FROM fts_example WHERE content MATCH 'foo'
The key points in this example are :
* The syntax for creating FTS3 tables is
CREATE VIRTUAL TABLE <table_name> USING fts3(<columns>)
where "<columns>" is a list of column names. Columns may be typed,
but the type information is ignored. If no columns are specified,
the default is a single column named "content". In addition, FTS3
tables have an implicit column called "docid" (or also "rowid") for
numbering the stored documents.
* Statements for inserting, updating or deleting records use the same
syntax as for regular SQLite tables.
* Full-text searches are specified with the "MATCH" operator, and an
operand which may be a single word, a word prefix ending with '*', a
list of words, a "phrase query" in double quotes, or a boolean
combination of the above.
* The builtin function "snippet(...)" builds a formatted excerpt of
the document text, where the words pertaining to the query are
highlighted.
There are many more details to building and searching FTS3 tables, so we
strongly invite you to read the full documentation at at
<
http://www.sqlite.org/fts3.html>.
Incompatible change : starting from version 1.31, "DBD::SQLite" uses the
new, recommended "Enhanced Query Syntax" for binary set operators (AND,
OR, NOT, possibly nested with parenthesis). Previous versions of
"DBD::SQLite" used the "Standard Query Syntax" (see
<
http://www.sqlite.org/fts3.html#section_3_2>). Unfortunately this is a
compilation switch, so it cannot be tuned at runtime; however, since
FTS3 was never advertised in versions prior to 1.31, the change should
be invisible to the vast majority of "DBD::SQLite" users. If, however,
there are any applications that nevertheless were built using the
"Standard Query" syntax, they have to be migrated, because the
precedence of the "OR" operator has changed. Conversion from old to new
syntax can be automated through DBD::SQLite::FTS3Transitional, published
in a separate distribution.
Tokenizers
The behaviour of full-text indexes strongly depends on how documents are
split into *tokens*; therefore FTS3 table declarations can explicitly
specify how to perform tokenization:
CREATE ... USING fts3(<columns>, tokenize=<tokenizer>)
where "<tokenizer>" is a sequence of space-separated words that triggers
a specific tokenizer, as explained below.
SQLite builtin tokenizers
SQLite comes with three builtin tokenizers :
simple
Under the *simple* tokenizer, a term is a contiguous sequence of
eligible characters, where eligible characters are all alphanumeric
characters, the "_" character, and all characters with UTF
codepoints greater than or equal to 128. All other characters are
discarded when splitting a document into terms. They serve only to
separate adjacent terms.
All uppercase characters within the ASCII range (UTF codepoints less
than 128), are transformed to their lowercase equivalents as part of
the tokenization process. Thus, full-text queries are
case-insensitive when using the simple tokenizer.
porter
The *porter* tokenizer uses the same rules to separate the input
document into terms, but as well as folding all terms to lower case
it uses the Porter Stemming algorithm to reduce related English
language words to a common root.
icu If SQLite is compiled with the SQLITE_ENABLE_ICU pre-processor
symbol defined, then there exists a built-in tokenizer named "icu"
implemented using the ICU library, and taking an ICU locale
identifier as argument (such as "tr_TR" for Turkish as used in
Turkey, or "en_AU" for English as used in Australia). For example:
CREATE VIRTUAL TABLE thai_text USING fts3(text, tokenize=icu th_TH)
The ICU tokenizer implementation is very simple. It splits the input
text according to the ICU rules for finding word boundaries and
discards any tokens that consist entirely of white-space. This may
be suitable for some applications in some locales, but not all. If
more complex processing is required, for example to implement
stemming or discard punctuation, use the perl tokenizer as explained
below.
Perl tokenizers
In addition to the builtin SQLite tokenizers, "DBD::SQLite" implements a
*perl* tokenizer, that can hook to any tokenizing algorithm written in
Perl. This is specified as follows :
CREATE ... USING fts3(<columns>, tokenize=perl '<perl_function>')
where "<perl_function>" is a fully qualified Perl function name (i.e.
prefixed by the name of the package in which that function is declared).
So for example if the function is "my_func" in the main program, write
CREATE ... USING fts3(<columns>, tokenize=perl 'main::my_func')
That function should return a code reference that takes a string as
single argument, and returns an iterator (another function), which
returns a tuple "($term, $len, $start, $end, $index)" for each term.
Here is a simple example that tokenizes on words according to the
current perl locale
sub locale_tokenizer {
return sub {
my $string = shift;
use locale;
my $regex = qr/\w+/;
my $term_index = 0;
return sub { # closure
$string =~ /$regex/g or return; # either match, or no more token
my ($start, $end) = ($-[0], $+[0]);
my $len = $end-$start;
my $term = substr($string, $start, $len);
return ($term, $len, $start, $end, $term_index++);
}
};
}
There must be three levels of subs, in a kind of "Russian dolls"
structure, because :
* the external, named sub is called whenever accessing a FTS3 table
with that tokenizer
* the inner, anonymous sub is called whenever a new string needs to be
tokenized (either for inserting new text into the table, or for
analyzing a query).
* the innermost, anonymous sub is called repeatedly for retrieving all
terms within that string.
Instead of writing tokenizers by hand, you can grab one of those already
implemented in the Search::Tokenizer module :
use Search::Tokenizer;
$dbh->do(<<"") or die DBI::errstr;
CREATE ... USING fts3(<columns>,
tokenize=perl 'Search::Tokenizer::unaccent')
or you can use "new" in Search::Tokenizer to build your own tokenizer.
Incomplete handling of utf8 characters
The current FTS3 implementation in SQLite is far from complete with
respect to utf8 handling : in particular, variable-length characters are
not treated correctly by the builtin functions "offsets()" and
"snippet()".
Database space for FTS3
FTS3 stores a complete copy of the indexed documents, together with the
fulltext index. On a large collection of documents, this can consume
quite a lot of disk space. If copies of documents are also available as
external resources (for example files on the filesystem), that space can
sometimes be spared --- see the tip in the Cookbook.
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 try_rtree
WHERE minLong >= ? AND maxLong <= ?
AND minLat >= ? AND maxLat <= ?
# ... and those that overlap query coordinates
my $overlap_sql = <<"";
SELECT id FROM try_rtree
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.
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".
Flags for sqlite3_open_v2
Support the full API of sqlite3_open_v2 (flags for opening the file).
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.
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 - 2012 Adam Kennedy.
Some parts copyright 2009 - 2012 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.
