Pull Request (PR) for new issue.

Summary of Changes

Fix no. 1:

This PR changes the index name of the combined index over columns (term,language) of table #__finder_terms from idx_term to idx_term_language for new installations on MySQL databases, i.e. in file mysql/joomla.sql, so it is consistent with how we name combined indexes over columns in general, and also consistent how it is done for PostgreSQL.

This also fixes the problem that an index with name idx_term is dropped and then added back with the same name in the update sql script mysql/4.0.0-2018-07-29.sql. The database schema checker does not support drop and and back an index with the same name, and it would end in a ping pong of index exists but should not and index does not exist but it should error from fix to next fix button run.

Fix no. 2:

The problem that the ping pong mentioned with the previous fix doesn't happen right now is because of another mistake in the same update script: The ALTER TABLE statement which contains the index changes handled here combines several changes, separated by comma. This is valid SQL of course, but not supported by the database schema checker/fixer. If we are lucky it checks the first statement, if we are unlucky it can result in an SQL syntax error, or the statements is not checked, depending if some spaces before and after these commas or not. For the checker/fixer there has to be one single ALTER TABLE statement for each change. This is also fixed by this PR here for MySQL. For PostgreSQL this has to be fixed, too. This is done in PR #26219 .

Fix no. 3:

In the same update sql script is another mistake: It adds an index with name language over the language column, in addition to the index idx_language on the same column. In file mysql/joomla.sql there is only index idx_language, so the additional index with name language in the update sql could be some copy and pase remainder. This PR fixes also this.

General remark on changing the SQL update script

Since we are not in beta yet and so don't have to support updates from 4.0-Alpha-x to 4.0-Alpha-y or between nightly builds, we can change the existing 4.0 update scripts (but of course not pre-4.0 scripts). Later when in beta this will not be allowed anymore, so now is a good time to fix it.

Testing Instructions

Code review.

I will see if I can add some instructions for a real test, if I get feedback that code review is not enough.

Expected result

Index names of table #__finder_terms are consistent in files mysql/joomla.sql and mysql/4.0.0-2018-07-29.sql, and the new index over columns (term,language) is added with the right, new name in file mysql/4.0.0-2018-07-29.sql, like it is already done for PostgreSQL.

For each index change of table #__finder_terms, one separate ALTER TABLE statement is used.

Actual result

See summary of changes at the top.

Documentation Changes Required

None.