Fix unique_constraints

[IceS2]

This PR aims to fix an issue with getting the wrong unique constraints from a table.

You can reproduce the issue by doing the following:

1. Create a schema SCHEMA_A
2. Create a table SCHEMA_A.TABLE with a constraint such as CONSTRAINT_NAME UNIQUE(COL1, COL2)
3. Create another schema SCHEMA_B
4. create another table SCHEMA_B.TABLEwith a constraint such as CONSTRAINT_NAME UNIQUE(COL1, COL3) *Important, the constraint name must be the same.

With that setup, if you run the query you can see that for both SCHEMA_A.TABLE and SCHEMA_B_TABLE you will find the constraint being: COL1, COL2, COL1, COL3.
This happens because we're doing a cross join and filtering only by the constraint name.

The PR changes the Query to actually do a join on:

• Constraint Name
• Schema Name
• Table Name
  in order to avoid this issue