SQLite partial indexes support

[Vincentv92]

Q	A
Type	improvement
Fixed issues

Summary

This adds support for partial indexes to the SQLitePlatform. Similar as the PostgresPlatform provides.

[SenseException]

Suggested change

	SELECT SUBSTR(sql, INSTR(sql, 'WHERE') + 6)
	SELECT SUBSTR(sql, INSTR(sql, 'WHERE') + LENGTH('WHERE '))

Question: Is this query somehow affected by the collation of a database so that an all uppercase WHERE would end up in a wrong result?

[Vincentv92]

Maybe i do not understand correctly, but if we are referring to the output of sql_master table it's documented here: https://www.sqlite.org/schematab.html#interpretation_of_the_schema_table it mentions it does some spaces conversion and keyword conversion. So I did some testing and if the partial is created with a lowercase where:

CREATE UNIQUE INDEX simple_partial_index ON person (id, name) where (id IS NULL)

instead of

CREATE UNIQUE INDEX simple_partial_index ON person (id, name) WHERE (id IS NULL)

it would output the lowercase where, since it was created that way.

SELECT SUBSTR(sql, INSTR(lower(sql), 'where') + LENGTH('where '))  FROM sqlite_master WHERE type = 'index'` AND name = (?)

would cover both cases. Since we are only checking in sqlite_master if we are dealing with a partial index.

I can modify the implementation but do we need an additional test which proves this? I can add it if we want it

[Vincentv92]

The reason why I stuck to uppercase is because dbal itself uses the where in uppercases, but it can be used in a context where the table has been created outside of dbal, which may slightly differ.

[Vincentv92]

I have added new commits which should resolve this