沒有其他記錄特定字段中選擇行

Question

Ciao的大家，我有如下表：

ID - 爲col_a - COL_B

我需要檢索所有具有記錄爲col_a = 1 COL_A = 1的COL_B不得有COL_A = 2的其他記錄。

你能幫助我嗎？

感謝

Answer 1

這是一個案例NOT EXISTS我想：

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) 

你也可以使用一個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