How can I select unique rows in a database over two columns? - sql

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.

Answer 2

This should do the trick - if the id fields are stored as integers then you will need to convert / cast into Varchars
SELECT 1 as id1,2 as id2,'TRUE' as qualifier,'AB' as data into #sampled
UNION ALL SELECT 1,2,NULL,'CD'
UNION ALL SELECT 1,3,NULL,'EF'
UNION ALL SELECT 1,3,NULL,'GH'
;WITH data as
(
SELECT
id1
,id2
,qualifier
,data
,SUM(CASE WHEN qualifier = 'TRUE' THEN 1 ELSE 0 END)
OVER (PARTITION BY id1 + '' + id2) as num_qualifier
from #sampled
)
SELECT
id1
,id2
,qualifier
,data
from data
where num_qualifier > 0

Answer 3

Select *
from yourTable
INNER JOIN (Select UserIDP1, UserIDP2 FROM yourTable WHERE Qualifier=TRUE) B
ON yourTable.UserIDP1 = B.UserIDP1 and YourTable.UserIDP2 = B.UserIDP2

Answer 4

How about a subquery as a where clause?
SELECT *
FROM theTable t1
WHERE CAST(t1.useridp1 AS VARCHAR) + CAST(t1.useridp2 AS VARCHAR) IN
(SELECT CAST(t2.useridp1 AS VARCHAR) + CAST(t.useridp2 AS VARCHAR)
FROM theTable t2
WHERE t2.qualified
);

Answer 5

This is a solution in mysql, but I believe it should transfer to sql server pretty easily. Use a subquery to pick out groups of (id1, id2) combinations with at least one True 'qualifier' row; then join that to the original table on (id1, id2).
mysql> SELECT u1.*
FROM users u1
JOIN (SELECT id1,id2
FROM users
WHERE qualifier
GROUP BY id1, id2) u2
USING(id1, id2);
+------+------+-----------+------+
| id1 | id2 | qualifier | data |
+------+------+-----------+------+
| 1 | 2 | 1 | aa |
| 1 | 2 | 0 | bb |
+------+------+-----------+------+
2 rows in set (0.00 sec)