MAN page from OpenSuSE 13.X perl-DBD-SQLite-1.54-42.1.x86_64.rpm

DBD::SQLite

Section: User Contributed Perl Documentation (3)
Updated: 2016-12-24
Index 

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 thatyou can find at <http://www.sqlite.org/>.

DBD::SQLite is a Perl DBI driver for SQLite, that includesthe entire thing in the distribution.So in order to get a fast transaction capable RDBMS working for yourperl project you simply have to install this module, and nothingelse.

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 iteasier 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 theSQL parser.

There's lots more to it, so please refer to the docs on the SQLite webpage, listed above, for SQL details. Also refer to DBI for detailson how to use DBI itself. The API works like every DBI module does.However, currently many statement attributes are not implemented orare limited by the typeless nature of the SQLite database. 

SQLITE VERSION

DBD::SQLite is usually compiled with a bundled SQLite library(SQLite version 3.13.0 as of this release) for consistency.However, a different version of SQLite may sometimes be used forsome 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 alsocheck "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" ofthe database file (with or without a parent directory) in the DBIconnection 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 ifit does not exist yet.

Although the database is stored in a single file, the directorycontaining the database file must be writable by SQLite because thelibrary will create several temporary files there.

If the filename $dbfile is ``:memory:'', then a private, temporaryin-memory database is created for the connection. This in-memorydatabase 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 additionalspecial filenames that begin with the ``:'' character. It is recommendedthat when a database filename actually does begin with a ``:'' characteryou should prefix the filename with a pathname such as ``./'' to avoidambiguity.

If the filename $dbfile is an empty string, then a private,temporary on-disk database will be created. This private database willbe 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 canonly 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, itcan't make the database read-only, and you'll see a warning (whichyou can hide by turning "PrintWarn" off). 

DBD::SQLite And File::Temp

When you use File::Temp to create a temporary file/directory forSQLite databases, you need to remember:

tempfile may be locked exclusively

You may want to use "tempfile()" to create a temporary databasefilename 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 temporarydirectory with "tempdir()" or "newdir()", you may have todisconnect databases explicitly before the temporary directoryis 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 cleanerfor 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 acrossa fork() system call into the child process. Problems will resultif you do.

You shouldn't (re)use a database handle you created (probably toset up a database schema etc) before you fork(). Otherwise, youmight 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), dependingon 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 withoutconflicting 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 SQLstatements such as length(x) will return the length of the column as a NULterminated string, rather than the size of the blob in bytes. In order tostore 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 functionwith 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 becomeslike 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 notalways been stored as numbers, so this *might* cause other obscureproblems. 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 forbind 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 fordetails.

<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 ornamed) 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 queryfor its internal data. These are specific to SQLite and are notlikely to work with other DBD libraries, but you may find some ofthese are quite useful, including:

journal_mode

You can use this pragma to change the journal mode for SQLitedatabases, maybe for better performance, or for compatibility.

Its default mode is "DELETE", which means SQLite uses a rollbackjournal to implement transactions, and the journal is deletedat the conclusion of each transaction. If you use "TRUNCATE"instead of "DELETE", the journal will be truncated, which isusually 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 afterclosing and reopening the database. In other words, once the "WAL"mode is set in an application or in a test script, the databasebecomes inaccessible by older clients. This tends to be an issuewhen you use a system "sqlite3" executable under a conservativeoperating 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 alsobe accessed by a very old SQLite client (prior to 3.3.0 releasedin Jan. 2006), you need to set this pragma to ON before you createa database.

reverse_unordered_selects

You can set this pragma to ON to reverse the order of results ofSELECT statements without an ORDER BY clause so that you can seeif applications are making invalid assumptions about the resultorder.

Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhancedits query optimizer and the order of results of a SELECT statementwithout an ORDER BY clause may be different from the one of theprevious versions.

synchronous

You can set set this pragma to OFF to make some of the operationsin SQLite faster with a possible risk of database corruptionin 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 foreignkeys, but the constraints has not been enforced. Now you can issuea "foreign_keys" pragma to enable this feature and enforce theconstraints, preferably as soon as you connect to a database andyou're not in a transaction:

  $dbh->do("PRAGMA foreign_keys = ON");

And you can explicitly disable the feature whenever you like byturning the pragma off:

  $dbh->do("PRAGMA foreign_keys = OFF");

As of this writing, this feature is disabled by default by theSQLite team, and by us, to secure backward compatibility, asthis feature may break your applications, and actually brokesome for us. If you have used a schema with foreign key constraintsbut haven't cared them much and supposed they're always ignored forSQLite, be prepared, and please do extensive testing to ensurethat your applications will continue to work when the foreign keyssupport 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 behavedifferently 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 youexplicitly begin a transaction, and when the transaction ended,you're supposed to go back to the auto-commit mode. To begin atransaction, call "begin_work" method, or issue a "BEGIN"statement. To end it, call "commit/rollback" methods, or issuethe 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 youexplicitly turn on the AutoCommit flag. You can explicitly issuea "BEGIN" statement (only when an actual transaction has notbegun 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 willautomatically begins 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 modeof 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", thatmeans, locks are not acquired until the first read or writeoperation, and thus it is possible that another thread or processcould create a separate transaction and write to the database afterthe "BEGIN" on the current thread has executed, and eventuallycause a ``deadlock''. To avoid this, DBD::SQLite internally issuesa "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 attributeto 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 begina 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 tocall ``finish'' in DBI method if you fetch all rows (probably in a loop).However, there are several exceptions to this rule, and rolling-backof an unfinished "SELECT" statement is one of such exceptionalcases.

SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements ina transaction (See <http://sqlite.org/lang_transaction.html> fordetails). 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 multiplestatements at a time. So if you pass a string that contains multiplestatements (a "dump") to a statement handle (via "prepare" or "do"),DBD::SQLite only processes the first statement, and discards therest.

If you need to process multiple statements at a time, set a "sqlite_allow_multiple_statements" attribute of a database handleto true when you connect to a database, and "do" method takes careof the rest (since 1.30_01, and without creating DBI's statementhandles internally since 1.47_01). If you do need to use "prepare"or "prepare_cached" (which I don't recommend in this case, becausetypically there's no placeholder nor reusable part in a dump),you can look at << $sth->{sqlite_unprepared_statements} >> to retrievewhat's left, though it usually contains nothing but white spaces. 

Performance

SQLite is fast, very fast. Matt processed his 72MB log file with it,inserting the data (400,000+ rows) by using transactions and onlycommitting 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 toreturn, 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 consideringswitching 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 youare using linux. Also you might want to set:

  PRAGMA synchronous = OFF

Which will prevent SQLite from doing fsync's when writing (whichslows down non-transactional writes significantly) at the expenseof some peace of mind. Also try playing with the cache_size pragma.

The memory usage of SQLite can also be tuned using the cache_sizepragma.

  $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 alltext strings coming out of the database (this feature is currently disabledfor perl < 5.8.5). For more details on the UTF-8 flag seeperlunicode. 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 retainblob-style behavior for some columns under "$dbh->{sqlite_unicode} = 1" (say, to store images in the database), you have to state soexplicitly using the 3-argument form of ``bind_param'' in DBI when doingupdates:

  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 multiplestatements at one go. This may be handy, but with performancepenalty. See above for details.

sqlite_use_immediate_transaction

If you set this to true, DBD::SQLite tries to issue a "beginimmediate transaction" (instead of "begin transaction") whennecessary. 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 valuesare number or not, and does not quote if they are numbers. See abovefor 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 commonmethods. 

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 anESCAPE character by including an 'Escape' attribute in \%attr. The $typeargument 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 isin. The default schema is 'main', temporary tables are in 'temp' and otherdatabases 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 thefirst argument of the methods is usually "undef", and you'll usuallyset "undef" for the second one (unless you want to know the primarykeys 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 withrespect to the ``foreign_key_info'' in DBI specification. All requested fieldsare 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), whenseveral 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.

Unfortunately, the DEFERRABILITY field is always "undef";as a matter of fact, deferrability clauses are supported by SQLite,but they can't be reported because the "PRAGMA foreign_key_list"tells nothing about them.

UNIQUE_OR_PRIMARY:Whether the column is primary or unique.

Note: foreign key support in SQLite must be explicitly turned on througha "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 withrespect to the ``statistics_info'' in DBI specification. All requested fieldsare 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 littletweak, but the use of func() method is now discouraged by the DBI authorfor various reasons (see DBI's document<http://search.cpan.org/dist/DBI/lib/DBI/DBD.pm#Using_install_method()_to_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 PRIMARYKEY 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_idmethod 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 SQLquery. The method's parameters are:

$name

The name of the function. This is the name of the function as it willbe 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 thecurrent 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', butwithout any implementation. The "DBD::SQLite" driverautomatically registers an implementation that performs standardperl regular expression matching, using current locale. So for exampleyou 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 iterateover 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 SQLquery as a COLLATE option for sorting. Such functions can also be registeredautomatically 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 willbe invoked whenever an undefined collation sequence is requiredfrom 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 justadd your collation sequences in the %DBD::SQLite::COLLATIONhash (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 usedfrom SQL. The method's parameters are:

$name

The name of the aggregate function, this is the name under which thefunction will be available from SQL.

$argc

This is an integer which tells the SQL parser how many arguments thefunction takes. If that number is -1, the function can take any numberof 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 shouldbe used to aggregate the rows in a particular group. The step() andfinalize() methods will be called upon the reference return bythe 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 wereprocessed and it should return the aggregate function's result. Whenthere is no rows in the aggregate, finalize() will be called rightafter 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 longrunning calls to SQLite.

An example use for this interface is to keep a GUI updated during alarge query. The parameters are:

$n_opcodes

The progress handler is invoked once for every $n_opcodesvirtual machine opcodes in SQLite.

$code_ref

Reference to the handler subroutine. If the progress handler returnsnon-zero, the SQLite operation is interrupted. This feature can be used toimplement a ``Cancel'' button on a GUI dialog box.

Set this argument to "undef" if you want to unregister a previousprogress handler.

 

$dbh->sqlite_commit_hook( $code_ref )

This method registers a callback function to be invoked whenever atransaction is committed. Any callback set by a previous call to"sqlite_commit_hook" is overridden. A reference to the previouscallback (if any) is returned. Registering an "undef" disables thecallback.

When the commit hook callback returns zero, the commit operation isallowed to continue normally. If the callback returns non-zero, thenthe commit is converted into a rollback (in that case, any attempt toexplicitly call "$dbh->rollback()" afterwards would yield anerror). 

$dbh->sqlite_rollback_hook( $code_ref )

This method registers a callback function to be invoked whenever atransaction is rolled back. Any callback set by a previous call to"sqlite_rollback_hook" is overridden. A reference to the previouscallback (if any) is returned. Registering an "undef" disables thecallback. 

$dbh->sqlite_update_hook( $code_ref )

This method registers a callback function to be invoked whenever a rowis updated, inserted or deleted. Any callback set by a previous call to"sqlite_update_hook" is overridden. A reference to the previouscallback (if any) is returned. Registering an "undef" disables thecallback.

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 withinthat table.

 

$dbh->sqlite_set_authorizer( $code_ref )

This method registers an authorizer callback to be invoked wheneverSQL statements are being compiled by the ``prepare'' in DBI method. Theauthorizer callback should return "DBD::SQLite::OK" to allow theaction, "DBD::SQLite::IGNORE" to disallow the specific action butallow the SQL statement to continue to be compiled, or"DBD::SQLite::DENY" to cause the entire SQL statement to be rejectedwith an error. If the authorizer callback returns any other value,then "prepare" call that triggered the authorizer will fail withan error message.

An authorizer is used when preparing SQL statements from an untrustedsource, to ensure that the SQL statements do not try to access datathey are not allowed to see, or that they do not try to executemalicious statements that damage the database. For example, anapplication may allow a user to enter arbitrary SQL queries forevaluation by a database. But the application does not want the userto be able to make arbitrary changes to the database. An authorizercould then be put in place while the user-entered SQL is beingprepared 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 forthe access attempt, or "undef" if this access attempt is directly fromtop-level SQL code.

 

$dbh->sqlite_backup_from_file( $filename )

This method accesses the SQLite Online Backup API, and will take a backup ofthe named database file, copying it to, and overwriting, your current databaseconnection. This can be particularly handy if your current connection is to thespecial :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 ofthe 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 wheneverSQL 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 statementfirst begins executing.

Additional callbacks might occur as each triggered subprogram isentered. The callbacks for triggers contain a UTF-8 SQL commentthat 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 whenevera 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 beregistered before creating a new virtual table using the module andbefore using a preexisting virtual table for the module.Virtual tables are explained in DBD::SQLite::VirtualTable. 

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 bundledlibrary 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 tosee if a string matches a pattern. These may be useful when youcreate 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 writinghooks or authorizer callbacks. For accessing such constants,the "DBD::SQLite" module must be explicitly "use"d at compiletime. For example, an authorizer that forbids anyDELETE 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 givenbelow; more information can be found adat <http://www.sqlite.org/c3ref/constlist.html>. 

Authorizer Return Codes

  OK  DENY  IGNORE

 

Action Codes

The ``set_authorizer'' method registers a callback function that isinvoked to authorize certain SQL statement actions. The firstparameter to the callback is an integer code that specifies whataction is being authorized. The second and third parameters to thecallback are strings, the meaning of which varies according to theaction code. Below is the list of action codes, together with theirassociated 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 arbitrarycomparison 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 arefolded to their lower case equivalents before the comparison isperformed. Note that only ASCII characters are case folded. SQLitedoes not attempt to do full UTF case folding due to the size of thetables required.

RTRIM

The same as binary, except that trailing space characters are ignored.

In addition, "DBD::SQLite" automatically installs thefollowing 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 fromthe database and passed to the collation function will be properlytagged with the utf8 flag; but this only works if the"sqlite_unicode" attribute is set before the first call toa perl collation sequence . The recommended way to activate unicodeis 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 isexposed through methods ``sqlite_create_collation'' and``sqlite_collation_needed''.

To avoid calling these functions every time a $dbh handle iscreated, "DBD::SQLite" offers a simpler interface through the%DBD::SQLite::COLLATION hash : just insert your owncollation functions in that hash, and whenever an unknowncollation name is encountered in SQL, the appropriate collationfunction will be loaded on demand from the hash. For example,here is a way to sort text values regardless of their accentedcharacters :

  use DBD::SQLite;  $DBD::SQLite::COLLATION{no_accents} = sub {    my ( $a, $b ) = map lc, @_;    tr[XXXXXXXXXXXXXXXXXXXXXXXXXXXX]      [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 predefinedin that same hash.

The COLLATION hash is a global registry within the current process;hence there is a risk of undesired side-effects. Therefore, toprevent action at distance, the hash is implemented as a ``write-only''hash, that will happily accept new entries, but will raise anexception if any attempt is made to override or delete a existingentry (including the builtin "perl" and "perllocale").

If you really, really need to change or delete an entry, you canalways grab the tied object underneath %DBD::SQLite::COLLATION ---but don't do that unless you really know what you are doing. Alsoobserve that changes in the global hash will not modify existingcollations in existing database handles: it will only affect newrequests for collations. In other words, if you want to changethe behaviour of a collation within an existing $dbh, youneed to call the ``create_collation'' method directly. 

FULLTEXT SEARCH

SQLite is bundled with an extension module for full-textindexing. Tables with this feature enabled can be efficiently queriedto find rows that contain one or more instances of some specifiedwords, 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 creatinga R-Tree, a special index for range and multidimensional queries. Thisallows users to create tables that can be loaded with (as an example)geospatial data such as latitude/longitude coordinates for buildings withina 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 $o