Renamed your PR so it better suites what you did.

Testing

Test the content search plugin (regular search). We need at least one test on PostgreSQL and on MySQLi (to make sure nothing broke).

on postgresql 9.3.5 works as expected without this PR

@test ok MySql here

@test and works with this pr too on postgresql 9.3.5

I am confused. I tested content search on postgres 9.3.5.0 and like @alikon I had no issue so what is the problem that this PR is fixing

Hello,

the difference is that with Postgresql 9.1 there was a change in regard to the group by of select Statements.

See https://wiki.postgresql.org/wiki/What%27s_new_in_PostgreSQL_9.1 - at the end of the page under "SQL and PL/PgSQL features" there is an example with the changes to the need of group by columns or not.

Similar to that query change there are quite a few in the whole core, who suffer the same problem. I found some of them in the other search plugins and so on.

One way would be to adapt all the SQL queryies, or the raise the overall Joomla requierment from PostgreSQL 8.3.18+ (http://www.joomla.org/about-joomla/technical-requirements.html) up to 9.1.

i've suspected something like this, and i'm agree to raise the DB joomla requirements, something similar arise with old mssql too, but i'm afraid that for B/C reason this can be done only for the 4.x,
some feedback from PLT on this?

Setting to needs review

@Humorlos This is a known issue which cannot be resolved in this version of Joomla. As it is specifically related to using a very old release of the database software on your server the only remedy is to update that to the latest release. Thank you for your report.