When someone issues this command:
ALTER TABLE test ADD UNIQUE (a, b);
What happens when:
1. A non-unique index is already defined over (a, b)
- Either add new index or promote existing one to unique?
2. A non-unique index is already defined over (b, a)
- As above?
3. A primary index is already defined over (a, b)
- ERROR: unique already implied by primary?
4. A primary index is already defined over (b, a)
- As above?
5. A unique index is already defined over (a, b)
- ERROR: unique index already exists over keys?
6. A unique index is already defined over (b, a)
- As above. Technically a different index, but effect as far as uniqueness is concerned is identical?
7. No index exists over (a, b) or (b, a)
- Create a new unique index over (a, b)?
Chris