Question

I have a relational table that connects two other tables based on their IDs. There can be duplicates for both columns – but there CANNOT be the same row twice. I handle the checking code side.

How do I remove duplicate rows (see below):

select * from people:

a | b
1   2
1   3
1   3
1   7
2   3
2   5
2   5
2   9

I want the result to be:

a | b
1   2
1   3
1   7
2   3
2   5
2   9

Answer 1

There can be duplicates for both columns – but there CANNOT be the same row twice

That’s a constraint on the table that you have not implemented. The constraint is a unique index on (a,b). If you had the index you would not have duplicates.

IMHO your best approach is to add the unique index to the table, using a temporary table to first remove the duplicates:

1. Copy person to person_temp
2. Delete all from person
3. Add unique index to person
4. Copy unique a,b from person_temp to `person.