INSERT SELECT WHERE 从常量插入多行

Question

我正在尝试插入多个行，这些行的值不是从现有 table 中获取的，而是使用 INSERT ... SELECT ... WHERE.

从外部连同 where 条件一起提供的

以下查询无效：

mysql> insert into `my_table` SELECT 1 as a, 2 as b, 3 as c from dual UNION ALL SELECT 4 , 5 , 6 from dual UNION ALL SELECT 7 , 8 , 9  from dual where 1>2 ;
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from my_table;
+---+---+------+
| a | b | c    |
+---+---+------+
| 1 | 2 |    3 |
| 4 | 5 |    6 |
+---+---+------+
2 rows in set (0.00 sec)

我想查询不插入任何行，因为 where 条件为假。但是，where 子句仅适用于最后一个 select，第 2 个 select 不受 where 子句影响。

如何更正？

Answer 1

只需将 UNION ALL 子查询包装在子查询中，以便将 WHERE 应用于整个结果集：

insert into `my_table` 
select a, b, c 
from (
   SELECT 1 as a, 2 as b, 3 as c 
   from dual 

   UNION ALL 

   SELECT 4 , 5 , 6 
   from dual 

   UNION ALL 

   SELECT 7 , 8 , 9  
   from dual ) as t
where a > b ;

INSERT SELECT WHERE 从常量插入多行

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