In MySQL you can query the version number "SELECT version();"

I don't know about other database drivers.

Thanks, it's a start :) For some reason I hadn't thought there would be ways through the SQL itself.

There isn't a specific DBI method for returning the db version although some time ago DBI added the get_info method which can be used to get db meta information. The get_info method is modeled on ODBC and is fully supported in DBD::ODBC like the following (stolen straight from DBD::ODBC's 20SqlServer.t test file):

    $dbms_name = $dbh->get_info(17);
    ok($dbms_name, "got DBMS name: $dbms_name");
    $dbms_version = $dbh->get_info(18);
    ok($dbms_version, "got DBMS version: $dbms_version");
    $m_dbmsversion = $dbms_version;
    $m_dbmsversion =~ s/^(\d+).*/$1/;
    ok($m_dbmsversion, "got DBMS major version: $m_dbmsversion");
    $driver_name = $dbh->get_info(6);
    ok($driver_name, "got Driver Name: $driver_name");
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However, other DBDs support get_info via a rather circuitous route (see generating the get_info method) which involves running some code through DBD::ODBC and the database's ODBC driver to find the get_info values then adding the results to the DBD. As a result, sometimes the results are not as dynamic as you might like i.e., the DBD would have to update the version numbers in the get_info structure when it connects and I suspect some don't. Also, I don't believe all DBDs have added full get_info support - DBD::Oracle only just got a reworked get_info recently for instance.

If you find a DBD which fails to support the get_info values you want then you can always rt it or even better fix it yourself and send the maintainer a patch.

You might also look at the private attribute information for each DBD - see private_attribute_info.

Beyond that, you are probably left with a database/DBD specific way for each database/DBD like the select you have been shown for MySQL.

Querying PostgreSQL, timtowtdi:

-- versions 7.4 thru 9:
# select substring(version() from E'^PostgreSQL (\\S+)') ; 
 substring 
-----------
 8.4.4
(1 row)

-- versions 7.4 thru 9:
# select current_setting('server_version'); 
 current_setting 
-----------------
 8.4.4
(1 row)

-- versions 8.2 thru 9:
# select current_setting('server_version_num');
 current_setting 
-----------------
 80404
(1 row)
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DBIx-Version looks unmaintained, but maybe it has some useful examples.

(update) There is info in DBD::Pg attributes as well:

perl -MDBI -e'my$dbh=DBI->connect("dbi:Pg:"); print $dbh->{pg_server_v
+ersion}, "\n"';
80404
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Then, the 2008 SQL standard prescribes a SQL_IMPLEMENTATION_INFO view which (in postgres) has this information:

select  implementation_info_name, character_value 
  from  information_schema.sql_implementation_info
 where  implementation_info_name ~ 'DBMS';

 implementation_info_name | character_value 
--------------------------+-----------------
 DBMS NAME                | PostgreSQL
 DBMS VERSION             | 08.04.0004
(2 rows)
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I seem to remember that, alas, this latter solution (although standard and therefore in principle the 'best') is not very widely available.