Question

Let us say we have the following table structure and values:

FooTable:
    foo1    foo2   timestamp
     1       1      1
     2       2      1
     2       1      2

Currently there is no primary key constraint on the table.

Question:

In Oracle, what is the best way to make foo1 the primary key of the table? Assume that:

1. No two rows will have both the same timestamp and foo1 value
2. The row with the latest timestamp takes precedence (other rows with the same foo1 value should be deleted).

Thus, here is the desired table structure after the query:

FooTable:
    foo1(pk)  foo2   timestamp
     1         1      1
     2         1      2

Note: The main problem is deleting the old duplicate rows. Once this is done, the following query can be used to setup the primary key without fear of duplicates:

alter table FooTable modify foo1 primary key;

Answer 1

Keep in mind that you’re destroying data here. Make sure that you have a good back-up of the database.

I don’t work with Oracle, but I think that this is generic enough. I don’t know if Oracle allows table aliases in the DELETE clause or not, so you may need to adjust for that:

DELETE FT1
FROM FooTable FT1
WHERE EXISTS (
    SELECT *
    FROM FooTable FT2
    WHERE
        FT2.foo1 = FT1.foo1 AND
        FT2.timestamp > FT1.timestamp
)