File Coverage

blib/lib/DBIx/Admin/CreateTable.pm

Criterion	Covered	Total	%
statement	9	95	9.4
branch	0	74	0.0
condition	0	8	0.0
subroutine	3	11	27.2
pod	4	8	50.0
total	16	196	8.1

package DBIx::Admin::CreateTable;

use strict;
use warnings;

use Moo;

has db_vendor =>
(
	is       => 'rw',
	default  => sub{return ''},
	required => 0,
);

has dbh =>
(
	is       => 'rw',
	isa      => sub{die "The 'dbh' parameter to new() is mandatory\n" if (! $_[0])},
	default  => sub{return ''},
	required => 0,
);

has primary_index_name =>
(
	is       => 'rw',
	default  => sub{return {} },
	required => 0,
);

has sequence_name =>
(
	is       => 'rw',
	default  => sub{return {} },
	required => 0,
);

has verbose =>
(
	is       => 'rw',
	default  => sub{return 0},
	required => 0,
);

our $VERSION = '2.10';

# -----------------------------------------------

sub BUILD
{
	my($self) = @_;

	$self -> db_vendor(uc $self -> dbh -> get_info(17) ); # SQL_DBMS_NAME.

	print STDERR __PACKAGE__, '. Db vendor ' . $self -> db_vendor . ". \n" if ($self -> verbose);

} # End of BUILD.

# --------------------------------------------------

sub create_table
{
	my($self, $sql, $arg) = @_;
	my($table_name)       = $sql;
	$table_name           =~ s/^\s*create\s+table\s+([a-z_0-9]+).+$/$1/is;

	$arg = {}                           if (! defined $arg);
	$$arg{$table_name} = {}             if (! defined $$arg{$table_name});
	$$arg{$table_name}{no_sequence} = 0 if (! defined $$arg{$table_name}{no_sequence});

	if (! $$arg{$table_name}{no_sequence})
	{
		my($sequence_name) = $self -> generate_primary_sequence_name($table_name);

		if ($sequence_name)
		{
			my($sql) = "create sequence $sequence_name";

			$self -> dbh -> do($sql);

			print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);

			if ($self -> dbh -> errstr() )
			{
				return $self -> dbh -> errstr(); # Failure.
			}

			print STDERR __PACKAGE__, ". Created sequence '$sequence_name'. \n" if ($self -> verbose);
		}
	}

	$self -> dbh -> do($sql);

	print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);

	if ($self -> dbh -> errstr() )
	{
		return $self -> dbh -> errstr(); # Failure.
	}

	print STDERR __PACKAGE__, ". Created table '$table_name'. \n" if ($self -> verbose);

	return ''; # Success.

} # End of create_table.

# --------------------------------------------------

sub drop_table
{
	my($self, $table_name, $arg) = @_;
	my($sequence_name)           = $self -> generate_primary_sequence_name($table_name);

	# Turn off RaiseError so we don't error if the sequence and table being deleted do not exist.
	# We do this by emulating local $$dbh{RaiseError}.

	my($dbh)          = $self -> dbh;
	my($raise_error)  = $$dbh{RaiseError};
	$$dbh{RaiseError} = 0;

	$self -> dbh($dbh);

	$arg = {}                           if (! defined $arg);
	$$arg{$table_name} = {}             if (! defined $$arg{$table_name});
	$$arg{$table_name}{no_sequence} = 0 if (! defined $$arg{$table_name}{no_sequence});

	my($sql);

	# For Oracle, drop the sequence before dropping the table.

	if ( ($self -> db_vendor eq 'ORACLE') && ! $$arg{$table_name}{no_sequence})
	{
		$sql = "drop sequence $sequence_name";

		$self -> dbh -> do($sql);

		print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);
		print STDERR __PACKAGE__, ". Dropped sequence '$sequence_name'. \n" if ($self -> verbose);
	}

	$sql = "drop table $table_name";

	$self -> dbh -> do($sql);

	print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);
	print STDERR __PACKAGE__, ". Dropped table '$table_name'. \n" if ($self -> verbose);

	# For Postgres, drop the sequence after dropping the table.

	if ( ($self -> db_vendor eq 'POSTGRESQL') && ! $$arg{$table_name}{no_sequence})
	{
		$sql = "drop sequence $sequence_name";

		$self -> dbh -> do($sql);

		print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);
		print STDERR __PACKAGE__, ". Dropped sequence '$sequence_name'. \n" if ($self -> verbose);
	}

	# Undo local $$dbh{RaiseError}.

	$$dbh{RaiseError} = $raise_error;

	$self -> dbh($dbh);

	return '';

} # End of drop_table.

# --------------------------------------------------

sub generate_primary_index_name
{
	my($self, $table_name) = @_;
	my($hashref) = $self -> primary_index_name;

	if (! $$hashref{$table_name})
	{
		$$hashref{$table_name} = $self -> db_vendor eq 'POSTGRESQL'
			? "${table_name}_pkey"
			: ''; # MySQL, Oracle, SQLite.

		$self -> primary_index_name($hashref);
	}

	return $$hashref{$table_name};

} # End of generate_primary_index_name.

# --------------------------------------------------

sub generate_primary_key_sql
{
	my($self, $table_name) = @_;
	my($sequence_name)     = $self -> generate_primary_sequence_name($table_name);
	my($primary_key)       =
	($self -> db_vendor eq 'MYSQL')
	? 'integer primary key auto_increment'
	: ($self -> db_vendor eq 'SQLITE')
	? 'integer primary key autoincrement'
	: $self -> db_vendor eq 'ORACLE'
	? 'integer primary key'
	: "integer primary key default nextval('$sequence_name')"; # Postgres.

	return $primary_key;

} # End of generate_primary_key_sql.

# --------------------------------------------------

sub generate_primary_sequence_name
{
	my($self, $table_name) = @_;
	my($hashref) = $self -> sequence_name;

	if (! $$hashref{$table_name})
	{
		$$hashref{$table_name} = $self -> db_vendor =~ /(?:MYSQL|SQLITE)/
			? ''
			: "${table_name}_id_seq"; # Oracle, Postgres.

		$self -> sequence_name($hashref);
	}

	return $$hashref{$table_name};

} # End of generate_primary_sequence_name.

# -----------------------------------------------
# Assumption: This code is only called in the case
# of Oracle and Postgres, and after importing data
# for all tables from a XML file (say).
# The mechanism used to import from XML does not
# activate the sequences because the primary keys
# are included in the data being imported.
# So, we have to reset the current values of the
# sequences up from their default values of 1 to
# the number of records in the corresponding table.
# If not, then the next call to nextval() would
# return a value of 2, which is already in use.

sub reset_all_sequences
{
	my($self, $arg) = @_;

	if ($self -> db_vendor ne 'MYSQL')
	{
		$self -> reset_sequence($_, $arg) for keys %{$self -> sequence_name};
	}

} # End of reset_all_sequences.

# -----------------------------------------------

sub reset_sequence
{
	my($self, $table_name, $arg) = @_;

	$arg = {}                           if (! defined $arg);
	$$arg{$table_name} = {}             if (! defined $$arg{$table_name});
	$$arg{$table_name}{no_sequence} = 0 if (! defined $$arg{$table_name}{no_sequence});

	if (! $$arg{$table_name}{no_sequence})
	{
		my($sequence_name) = $self -> generate_primary_sequence_name($table_name);
		my($sth)           = $self -> dbh -> prepare("select count(*) from $table_name");

		$sth -> execute();

		my($max) = $sth -> fetch();
		$max     = $$max[0] || 0;
		my($sql) = "select setval('$sequence_name', $max)";

		$sth -> finish();
		$self -> dbh -> do($sql);

		print STDERR __PACKAGE__, ". SQL: $sql. \n" if ($self -> verbose);
		print STDERR __PACKAGE__, ". Reset table '$table_name', sequence '$sequence_name' to $max. \n" if ($self -> verbose);
	}

} # End of reset_sequence.

# --------------------------------------------------

1;

=head1 NAME

DBIx::Admin::CreateTable - Create and drop tables, primary indexes, and sequences

=head1 Synopsis

	#!/usr/bin/env perl

	use strict;
	use warnings;

	use DBI;
	use DBIx::Admin::CreateTable;

	# ----------------

	my($dbh)        = DBI -> connect(...);
	my($creator)    = DBIx::Admin::CreateTable -> new(dbh => $dbh, verbose => 1);
	my($table_name) = 'test';

	$creator -> drop_table($table_name);

	my($primary_key) = $creator -> generate_primary_key_sql($table_name);

	$creator -> create_table(<
	create table $table_name
	(
		id $primary_key,
		data varchar(255)
	)
	SQL

See also xt/author/fk.t in L.

=head1 Description

C is a pure Perl module.

Database vendors supported: MySQL, Oracle, Postgres, SQLite.

Assumptions:

=over 4

=item Every table has a primary key

=item The primary key is a unique, non-null, integer

=item The primary key is a single column

=item The primary key column is called 'id'

=item If a primary key has a corresponding auto-created index, the index is called 't_pkey'

This is true for Postgres, where declaring a column as a primary key automatically results in the creation
of an associated index for that column. The index is named after the table, not after the column.

=item If a table 't' (with primary key 'id') has an associated sequence, the sequence is called 't_id_seq'

This is true for both Oracle and Postgres, which use sequences to populate primary key columns. The sequences
are named after both the table and the column.

=back

=head1 Constructor and initialization

new(...) returns an object of type C.

This is the class contructor.

Usage: DBIx::Admin::CreateTable -> new().

This method takes a set of parameters. Only the dbh parameter is mandatory.

For each parameter you wish to use, call new as new(param_1 => value_1, ...).

=over 4

=item dbh

This is a database handle, returned from the DBI connect() call.

This parameter is mandatory.

There is no default.

=item verbose

This is 0 or 1, to turn off or on printing of progress statements to STDERR.

This parameter is optional.

The default is 0.

=back

=head1 Method: create_table($sql, $arg)

Returns '' (empty string) if successful and DBI errstr() if there is an error.

$sql is the SQL to create the table.

$arg is an optional hash ref of options per table.

The keys are table names. The only sub-key at the moment is...

=over 4

=item no_sequence

	$arg = {$table_name_1 => {no_sequence => 1}, $table_name_2 => {no_sequence => 1} };

can be used to tell create_table not to create a sequence for the given table.

You would use this on a CGI::Session-type table called 'sessions', for example,
when using Oracle or Postgres. With MySQL there would be no sequence anyway.

You would also normally use this on a table called 'log'.

The reason for this syntax is so you can use the same hash ref in a call to reset_all_sequences.

=back

Usage with CGI::Session:

	my($creator)    = DBIx::Admin::CreateTable -> new(dbh => $dbh, verbose => 1);
	my($table_name) = 'sessions';
	my($type)       = $creator -> db_vendor() eq 'ORACLE' ? 'long' : 'text';

	$creator -> drop_table($table_name);
	$creator -> create_table(< {no_sequence => 1} });
	create table $table_name
	(
		id char(32) primary key,
		a_session $type not null
	)
	SQL

Typical usage:

	my($creator)     = DBIx::Admin::CreateTable -> new(dbh => $dbh, verbose => 1);
	my($table_name)  = 'test';
	my($primary_key) = $creator -> generate_primary_key_sql($table_name);

	$creator -> drop_table($table_name);
	$creator -> create_table(<
	create table $table_name
	(
		id $primary_key,
		data varchar(255)
	)
	SQL

The SQL generated by this call to create_table() is spelled-out in the (SQL) table below.

Action:

	Method:   create_table($table_name, $arg).
	Comment:  Creation of tables and sequences.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|---------------------------------------------------+
	|          |            Action for $$arg{$table_name}          |
	|  Vendor  |      {no_sequence => 0}      | {no_sequence => 1} |
	+----------|------------------------------|--------------------+
	|  MySQL   |        Create table          |    Create table    |
	+----------|------------------------------|--------------------+
	|  Oracle  | Create sequence before table |    Create table    |
	+----------|------------------------------|--------------------+
	| Postgres | Create sequence before table |    Create table    |
	+----------|------------------------------|--------------------+
	|  SQLite  |        Create table          |    Create table    |
	+----------|------------------------------|--------------------+

SQL:

	Method:   create_table($table_name, $arg).
	Comment:  SQL generated.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|-------------------------------------------------------------------------------------+
	|          |                            SQL for $$arg{$table_name}                               |
	|  Vendor  |              {no_sequence => 0}          |            {no_sequence => 1}            |
	+----------|------------------------------------------|------------------------------------------+
	|  MySQL   |         create table $table_name         |         create table $table_name         |
	|          |        (id integer primary key           |        (id integer auto_increment        |
	|          |              auto_increment,             |              primary key,                |
	|          |           data varchar(255) )            |           data varchar(255) )            |
	+----------|------------------------------------------|------------------------------------------+
	|  Oracle  |  create sequence ${table_name}_id_seq &  |                                          |
	|          |        create table $table_name          |        create table $table_name          |
	|          |        (id integer primary key,          |        (id integer primary key,          |
	|          |           data varchar(255) )            |           data varchar(255) )            |
	+----------|------------------------------------------|------------------------------------------+
	| Postgres |  create sequence ${table_name}_id_seq &  |                                          |
	|          |         create table $table_name         |         create table $table_name         |
	|          |         (id integer primary key          |         (id integer primary key          |
	|          | default nextval("${table_name}_id_seq"), | default nextval("${table_name}_id_seq"), |
	|          |            data varchar(255) )           |            data varchar(255) )           |
	+----------|------------------------------------------|------------------------------------------+
	|  SQLite  |         create table $table_name         |         create table $table_name         |
	|          |        (id integer primary key           |        (id integer autoincrement         |
	|          |              autoincrement,              |              primary key,                |
	|          |           data varchar(255) )            |           data varchar(255) )            |
	+----------|------------------------------------------|------------------------------------------+

=head1 Method: db_vendor()

Returns an upper-case string identifying the database vendor.

Return string:

	Method:   db_vendor(db_vendor).
	Comment:  Value returned.
	+----------|------------+
	|  Vendor  |   String   |
	+----------|------------+
	|  MySQL   |   MYSQL    |
	+----------|------------+
	|  Oracle  |   ORACLE   |
	+----------|------------+
	| Postgres | POSTGRESQL |
	+----------|------------+
	|  SQLite  |   SQLITE   |
	+----------|------------+

=head1 Method: drop_table($table_name, $arg)

Returns '' (empty string).

$table_name is the name of the table to drop.

$arg is an optional hash ref of options, the same as for C.

Action:

	Method:  drop_table($table_name, $arg).
	Comment: Deletion of tables and sequences.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|-------------------------------------------------+
	|          |          Action for $$arg{$table_name}          |
	|  Vendor  |    {no_sequence => 0}      | {no_sequence => 1} |
	+----------|----------------------------|--------------------+
	|  MySQL   |         Drop table         |     Drop table     |
	+----------|----------------------------|--------------------+
	|  Oracle  | Drop sequence before table |     Drop table     |
	+----------|----------------------------|--------------------+
	| Postgres | Drop sequence after table  |     Drop table     |
	+----------|----------------------------|--------------------+
	|  SQLite  |         Drop table         |     Drop table     |
	+----------|----------------------------|--------------------+

SQL:

	Method:   drop_table($table_name, $arg).
	Comment:  SQL generated.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|---------------------------------------------------------------+
	|          |                        SQL for $$arg{$table_name}             |
	|  Vendor  |          {no_sequence => 0}          |   {no_sequence => 1}   |
	+----------|--------------------------------------|------------------------+
	|  MySQL   |        drop table $table_name        | drop table $table_name |
	+----------|--------------------------------------|------------------------+
	|  Oracle  | drop sequence ${table_name}_id_seq & |                        |
	|          |        drop table $table_name        | drop table $table_name |
	+----------|--------------------------------------|------------------------+
	| Postgres |       drop table $table_name &       | drop table $table_name |
	|          |  drop sequence ${table_name}_id_seq  |                        |
	+----------|--------------------------------------|------------------------+
	|  SQLite  |        drop table $table_name        | drop table $table_name |
	+----------|--------------------------------------|------------------------+

Note: drop_table() turns off RaiseError so we do not error if the sequence and table being deleted do not exist.
This is new in V 2.00.

=head1 Method: generate_primary_index_name($table_name)

Returns the name of the index corresponding to the primary key for the given table.

The module does not call this method.

SQL:

	Method:  generate_primary_index_name($table_name).
	Comment: Generation of name of the index for the primary key.
	+----------|--------------------+
	|  Vendor  |        SQL         |
	+----------|--------------------+
	|  MySQL   |                    |
	+----------|--------------------+
	|  Oracle  |                    |
	+----------|--------------------+
	| Postgres | ${table_name}_pkey |
	+----------|--------------------+
	|  SQLite  |                    |
	+----------|--------------------+

=head1 Method: generate_primary_key_sql($table_name)

Returns partial SQL for declaring the primary key for the given table.

See the Synopsis for how to use this method.

SQL:

	Method:   generate_primary_key_sql($table_name).
	Comment:  Generation of partial SQL for primary key.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|-----------------------------------------------------+
	|  Vendor  |                       SQL                           |
	+----------|-----------------------------------------------------+
	|  MySQL   |         integer primary key auto_increment          |
	+----------|-----------------------------------------------------+
	|  Oracle  |               integer primary key                   |
	+----------|-----------------------------------------------------+
	| Postgres | integer primary key default nextval($sequence_name) |
	+----------|-----------------------------------------------------+
	|  SQLite  |         integer primary key autoincrement          |
	+----------|-----------------------------------------------------+

=head1 Method: generate_primary_sequence_name($table_name)

Returns the name of the sequence used to populate the primary key of the given table.

SQL:

	Method:  generate_primary_sequence_name($table_name).
	Comment: Generation of name for sequence.
	+----------|----------------------+
	|  Vendor  |         SQL          |
	+----------|----------------------+
	|  MySQL   |                      |
	+----------|----------------------+
	|  Oracle  | ${table_name}_id_seq |
	+----------|----------------------+
	| Postgres | ${table_name}_id_seq |
	+----------|----------------------+
	|  SQLite  |                      |
	+----------|----------------------+

=head1 Method: reset_all_sequences($arg)

Returns nothing.

Resets the primary key sequence for all tables, except those marked by $arg as not having a sequence.

Note: This method only works if called against an object which knows the names of all tables and sequences.
This means you must have called at least one of these, for each table:

=over

=item create_table

=item drop_table

=item generate_primary_key_sql

=item generate_primary_sequence_name

=back

$arg is an optional hash ref of options, the same as for C.

Summary:

	Method:  reset_all_sequences($arg).
	Comment: Reset all sequences.
	+----------|-------------------------------------------------------+
	|  Vendor  |                      Action                           |
	+----------|-------------------------------------------------------+
	|  MySQL   |                    Do nothing                         |
	+----------|-------------------------------------------------------+
	|  Oracle  | Call reset_sequence($table_name, $arg) for all tables |
	+----------|-------------------------------------------------------+
	| Postgres | Call reset_sequence($table_name, $arg) for all tables |
	+----------|-------------------------------------------------------+
	|  SQLite  |                    Do nothing                         |
	+----------|-------------------------------------------------------+

=head1 Method: reset_sequence($table_name, $arg)

Returns nothing.

Resets the primary key sequence for the given table, except if it is marked by $arg as not having a sequence.

$arg is an optional hash ref of options, the same as for C.

Summary:

	Method:   reset_sequence($table_name, $arg).
	Comment:  Reset one sequence.
	Sequence: The value of the sequence is set to the number of records in the table.
	+----------|-----------------------------------------+
	|          |      Action for $$arg{$table_name}      |
	|  Vendor  | {no_sequence => 0} | {no_sequence => 1} |
	+----------|--------------------|--------------------+
	|  MySQL   |    Do nothing      |     Do nothing     |
	+----------|--------------------|--------------------+
	|  Oracle  | Set sequence value |     Do nothing     |
	+----------|--------------------|--------------------+
	| Postgres | Set sequence value |     Do nothing     |
	+----------|--------------------|--------------------+
	|  SQLite  |    Do nothing      |     Do nothing     |
	+----------|--------------------|--------------------+

=head1 FAQ

=head2 Which versions of the servers did you test?

	Versions as at 2014-03-07
	+----------|------------+
	|  Vendor  |     V      |
	+----------|------------+
	|  MariaDB |   5.5.36   |
	+----------|------------+
	|  Oracle  | 10.2.0.1.0 | (Not tested for years)
	+----------|------------+
	| Postgres |   9.1.12   |
	+----------|------------+
	|  SQLite  |   3.7.17   |
	+----------|------------+

=head2 Do all database servers accept the same 'create table' commands?

No. You have been warned.

References for 'Create table':
L.
L.
L.

Consider these:

	create table one
	(
		id   integer primary key autoincrement,
		data varchar(255)
	) $engine

	create table two
	(
		id      integer primary key autoincrement,
		one_id  integer not null,
		data    varchar(255),
		foreign key(one_id) references one(id)
	) $engine

Putting the 'foreign key' clause at the end makes it a table constraint. Some database servers, e.g. MySQL and Postgres,
allow you to attach it to a particular column, as explained next.

=over 4

=item o MySQL

The creates work as given, where $engine eq 'engine = innodb'.

Further, you can re-order the clauses in the 2nd create:

	create table two
	(
		id      integer primary key autoincrement,
		one_id  integer not null,
		foreign key(one_id) references one(id),
		data    varchar(255)
	) $engine

This also works, where $engine eq 'engine = innodb'.

However, if you use:

	create table two
	(
		id      integer primary key autoincrement,
		one_id  integer not null references one(id),
		data    varchar(255)
	) $engine

Then the 'references' (foreign key) clause is parsed but discarded, even with 'engine = innodb'.

=item o Postgres

The creates work as given, where $engine = ''.

And you can re-order the clauses, as in the first example for MySQL.

=item o SQLite

The creates work as given, where $engine = ''.

But if you re-order the clauses:

	create table two
	(
		id      integer primary key autoincrement,
		one_id  integer not null,
		foreign key(one_id) references one(id),
		data    varchar(255)
	) $engine

Then you get a syntax error.

However, if you use:

	create table two
	(
		id      integer primary key autoincrement,
		one_id  integer not null references one(id),
		data    varchar(255)
	) $engine

Then the 'references' (foreign key) clause is parsed, and it does create a foreign key relationship.

=back

Do not forget this when using SQLite:

	$dbh -> do('pragma foreign_keys = on') if ($dsn =~ /SQLite/i);

=head2 Do I include the name of an auto-populated column in an insert statement?

Depends on the server. Some databases, e.g. Postgres, do I want the name of the primary key
in the insert statement if the server is to generate a value for a column.

SQL for insert:

	Comment: SQL for insertion of rows containing auto-populated values.
	Sequence: See generate_primary_sequence_name($table_name).
	+----------|-----------------------------------------------------------------------+
	|  Vendor  |                                   SQL                                 |
	+----------|-----------------------------------------------------------------------+
	|  MySQL   |               insert into $table_name (data) values (?)               |
	+----------|-----------------------------------------------------------------------+
	|  Oracle  | insert into $table_name (id, data) values ($sequence_name.nextval, ?) |
	+----------|-----------------------------------------------------------------------+
	| Postgres |               insert into $table_name (data) values (?)               |
	+----------|-----------------------------------------------------------------------+
	|  SQLite  |          insert into $table_name (id, data) values (undef, ?)         |
	+----------|-----------------------------------------------------------------------+

=head2 Do I have to use a sequence to populate a primary key?

Well, no, actually. See next question.

=head2 How to I override the auto-populated value for a primary key column?

By including the name and the value in the insert statement.

SQL for insert:

	Comment: SQL for insertion of rows overriding auto-populated values.
	+----------|--------------------------------------------------+
	|  Vendor  |                     SQL                          |
	+----------|--------------------------------------------------+
	|  MySQL   | insert into $table_name (id, data) values (?, ?) |
	+----------|--------------------------------------------------+
	|  Oracle  | insert into $table_name (id, data) values (?, ?) |
	+----------|--------------------------------------------------+
	| Postgres | insert into $table_name (id, data) values (?, ?) |
	+----------|--------------------------------------------------+
	|  SQLite  | insert into $table_name (id, data) values (?, ?) |
	+----------|--------------------------------------------------+

=head2 Are primary keys always not null and unique?

Yes. All servers document primary key as meaning both non null and unique.

=head2 See Also

L.

L.

=head1 Version Numbers

Version numbers < 1.00 represent development versions. From 1.00 up, they are production versions.

=head1 Support

Log a bug on RT: L.

=head1 Author

C was written by Ron Savage [e-mail]> in 2006.

Home page: http://savage.net.au/index.html

=head1 Copyright

	Australian copyright (c) 2006,  Ron Savage.
	All Programs of mine are 'OSI Certified Open Source Software';
	you can redistribute them and/or modify them under the terms of
	the Artistic or the GPL licences, copies of which is available at:
	http://www.opensource.org/licenses/index.html

=cut