[MYSQL] Fix columnInfo showing column multiple times.

[Nitwel]

closes #63

[rijkvanzanten]

@oreilles looking good>?

[oreilles]

I would do a left join lateral with limit 1 instead, that would avoid calculating the row number and adding the last where close.
EDIT: apparently not possible, I thought it was Postgres, LATERAL only was added to MySQL in 8.0.

[oreilles]

We should add a test for this adding multiple indicies on one column. And for other vendors as well