mysql - 在 SQL 中，如何只获取整个表的单个列中具有相同值的条目？

Question

所以我坚持尝试制作一个 SQL 来获取每个对特定 COLUMN 具有相同值的 ROW。

例子:
表:买家

aID | bID                        aID | bID
 1  |  3                          1  |  3 
 1  |  4                          1  |  2
 1  |  2                          2  |  2
 1  |  5                          1  |  4    this one also should return aID = 1
                                       since aID =1 is present for every different bID

我想我很接近:

SELECT aID
  FROM buyers
 WHERE COUNT(bID) = (SELECT S1.aID
                       FROM buyers S1, 
                            buyers S2
                      WHERE S1.aID = S2.bID
                        AND S2.bID <> S1.bID)

它必须在每一行中的一列中，否则就得不到它，所以如果一个 aID 不同，那就不要得到它。 aID 必须与每个 bID

匹配

Answer 1

SELECT aID
FROM buyers
GROUP BY aID
HAVING COUNT(*) = (SELECT COUNT(distinct bID) FROM buyers)

FIDDLE

这假设每个 aID,bID 组合都是唯一的。如果 bID 可以针对相同的 aID 重复，则需要执行以下操作:

SELECT aID
FROM (SELECT DISTINCT aID, bID FROM buyers)
GROUP BY aID
HAVING COUNT(*) = (SELECT COUNT(distinct bID) FROM buyers)