Question

说我有一条SQL语句：

SELECT * 
FROM MY_TABLE 
WHERE MY_FIELD IN ('AAA','BBB','CCC', 'DDD');

我的桌子是：

ID FIELD1
1  AAA
2  CCC
3  DDD
4  FFF

上面的sql语句会给我数据库中的3条记录。

我的问题是如何更改我的SQL语句以找到它找不到的记录？（即告诉我BBB没有匹配）

Answer 1

您需要LEFT JOIN，NOT IN或NOT EXISTS：

SELECT v.* 
FROM (SELECT 'AAA' as f FROM DUAL UNION ALL
      SELECT 'BBB' as f FROM DUAL UNION ALL
      SELECT 'CCC' as f FROM DUAL UNION ALL
      SELECT 'DDD' as f FROM DUAL
     ) v LEFT JOIN
     MY_TABLE t
     ON v.f = t.my_field
WHERE t.my_field IS NULL;

Answer 2

$calculator = new calculator();
echo $calculator->addition(10)->multiplication(2)->getResult(); // 20

如何确定在IN子句中找不到哪条记录

2 个答案: