从3列表中选择所有记录，其中2个特定列中有重复项

Question

Let's say I have the following table in SQL Server (tbl1):

Num     Zip     Rating
1       75235   100
2       77234   50
3       77234   100
4       77234   100
5       77234   100
6       75235   75
7       76076   25
8       76076   25 
9       76076   50
10      75234   25
11      75234   50
12      75234   50

I want to select all of the rows where the Zip and Rating columns combined have duplicates. In this case, that would be rows 3, 4, 5, 7, 8, 11, and 12. How would I do that?

Answer 1

SELECT *
FROM tbl1 t1
WHERE (
    SELECT COUNT (*)
    FROM tbl1 t2
    WHERE t2.Zip = t1.Zip AND t2.Rating = t1.Rating
) > 1

Answer 2

Find all rows that have at least one exact duplicate with all equal values, except for the Num column which should be different:

SELECT *
FROM tbl1 T1
WHERE EXISTS (
    SELECT 1
    FROM tbl1 T2
    WHERE T2.Zip    = T1.Zip
    AND   T2.Rating = T1.Rating
    AND   T2.Num   <> T1.Num
)