Fix Export when full group by mode is used

[eileenmcnaughton]

Overview

Fixes an export performance issue in mysql Full Group By mode

Before

Running ExportIMTest horrendously slow with Full Group By enabled due to returning 7776 rows for php processing rather than 1

After

Test works quickly. Query is marked as not meeting the full group by standard using disable & re-enabled full group by.

Technical Details

After upgrading locally to mysql 5.7 I found that the exportIM test
was taking so long locally that I was killing it rather than finding
out how long it would take.

Digging into it I found that we were changing the query so that
attempts to group by contact ID were being nullified when full group by
is enabled. This meant that we were winding up with
7776 rows being retrieved to reflect a grid of permutations, which was
being iterated down to 1 in php.

In general the practice of altering the group by to meet this new
standard is one that we determined to be
causing problems and we discontinued / rolled back

Comments

Note test coverage is strong across the changed code

@seamuslee001

[civibot]

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[seamuslee001]

This looks good test coverage seems to be reasonable. The changes make sense and are in line with what we have been doing Merging