Primitive Keys: Support CAST in join criteria

[big-andy-coates]

Previously, as all keys were of type STRING you could join on two columns of different types, e.g. a STRING column that you know to contain a number with an INTEGER column, or an INTEGER column with a BIGINT column.

With primitive key support this is no longer the case. The STRING containing a number won't necessarily be the same as a INTEGER. Hence the join is not allowed.

This can break users existing joins, with no easy way for them to fix because we don't support arbitrary expressions in the join criteria, i,.e. they can't do:

SELECT * FROM A JOIN B ON A.ID = CAST(B.ID AS INTEGER);

We could consider supporting casts, or just any expression, in the join criteria.

[agavra]

Dropping a note here, but I need to explore more in depth - I'm wondering if this was properly implemented in first place. The partitioning strategy for Strings may not be the same as for Integers (for example) so the co-partitioning requirement may have been broken to begin with.

[big-andy-coates]

As discussed, I still think its worthwhile