我如何 SELECT 只有表 b 中每个外键给定列的值都相同的行？

Question

I have a table that just has ID's. Another table that has ID plus a couple other columns. One such column is [set], for reference.

I am trying to build a join query on only the ID's in table2 that have the same value for every row in column [set], not just ID'S that have a duplicate value in [set] plus another different value. So, each ID in table2 can have multiple rows.

table1

[id]
a1
a2

table2

[id]	[op]	[set]
a1	22	cut
a1	21	cut
a2	23	cut
a2	25	cut
a2	24	slice

In the given example, 'a2' would not fit the criteria because the values in column [set] are not all the same.

My query isn't working.

SELECT DISTINCT(A.ID)
FROM TABLE1 A
INNER JOIN TABLE2 B ON A.ID = B.ID
GROUP BY A.ID, B.SET
HAVING COUNT(DISTINCT(B.SET)) =1

Answer 1

You're grouping by id and set , so by definition within each group, there will be just one value for set . Remove it from the group by clause and you should be OK. Also, not that since you're grouping by the id , you don't need a distinct on it:

SELECT   A.ID -- Distinct removed. It's not wrong, just redundant
FROM     TABLE1 A
INNER    JOIN TABLE2 B ON A.ID = B.ID
GROUP BY A.ID -- Grouping by b.set removed
HAVING   COUNT(DISTINCT(B.SET)) = 1