Question

I have found similar solutions online but none that I’ve been able to apply to my specific problem.

I’m trying to “unique-ify” data from one table to another. In my original table, data looks like the following:

USERIDP1    USERIDP2     QUALIFIER     DATA
1           2            TRUE          AB
1           2                          CD
1           3                          EF
1           3                          GH

The user IDs are composed of two parts, USERIDP1 and USERIDP2 concatenated. I want to transfer all the rows that correspond to a user who has QUALIFIER=TRUE in ANY row they own, but ignore users who do not have a TRUE QUALIFIER in any of their rows.

To clarify, all of User 12’s rows would be transferred, but not User 13’s. The output would then look like:

USERIDP1    USERIDP2     QUALIFIER     DATA
1           2            TRUE          AB
1           2                          CD

So basically, I need to find rows with distinct user ID components (involving two unique fields) that also possess a row with QUALIFIER=TRUE and copy all and only all of those users’ rows.

Answer 1

Although this nested query will be very slow for large tables, this could do it.

SELECT DISTINCT X.USERIDP1, X.USERIDP2, X.QUALIFIER, X.DATA
FROM YOUR_TABLE_NAME AS X
WHERE EXISTS (SELECT 1 FROM YOUR_TABLE_NAME AS Y WHERE Y.USERIDP1 = X.USERIDP1
              AND Y.USERIDP2 = X.USERIDP2 AND Y.QUALIFIER = TRUE)

It could be written as an inner join with itself too:

SELECT DISTINCT X.USERIDP1, X.USERIDP2, X.QUALIFIER, X.DATA
FROM YOUR_TABLE_NAME AS X
INNER JOIN YOUR_TABLE_NAME AS Y ON Y.USERIDP1 = X.USERIDP1
                                AND Y.USERIDP2 = X.USERIDP2 AND Y.QUALIFIER = TRUE

For a large table, create a new auxiliary table containing only USERIDP1 and USERIDP2 columns for rows that have QUALIFIER = TRUE and then join this table with your original table using inner join similar to the second option above. Remember to create appropriate indexes.