選擇特定字段沒有其他記錄的行

Question

大家好，我有下表：

ID-COL_A-COL_B

我需要檢索所有具有COL_A = 1的記錄和具有COL_A = 1的COL_B不能包含具有COL_A = 2的其他記錄。

你可以幫幫我嗎？

謝謝

Answer 1

這是一個情況下NOT EXISTS我認為：

SELECT *
FROM mytable AS t1
WHERE COL_A = 1 AND 
      NOT EXISTS (SELECT 1
                  FROM mytable
                  WHERE t1.COL_B = t2.COL_B AND COL_A = 2)  

您也可以使用LEFT JOIN ：

SELECT t1.*
FROM mytable AS t1
LEFT JOIN mytable AS t2 ON t1.COL_B = t2.COL_B AND t2.COL_A = 2
WHERE t1.COL_A = 1 AND t2.COL_A IS NULL