结果中的MySQL子查询

我想使用我的表上查询的ID从我的表2中选择所有字段行

  SELECT field_b
  FROM my_table_2
  WHERE my_id_2 IN (
         SELECT my_id FROM my_table WHERE field_a = 1234
  );

执行上述查询时，我得到

错误1054（42S22）“/ALL/ANY子查询”中的未知列“my_id_2”

以下是我的表格示例供参考：

  mysql> select * from my_table;
    +-------+---------+
    | my_id | field_a |
    +-------+---------+
    |     1 |    1234 |
    +-------+---------+
    |     2 |    1234 |
    +-------+---------+
    2 row in set (0.00 sec)

mysql> select * from my_table_2;
+-------+-----------+
| my_id_2 | field_b |
+---------+---------+
|     1   |  5678   |
+-------+-----------+
1 row in set (0.00 sec)

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可以将该查询重写为简单的联接操作：

SELECT field_b
FROM my_table_2
INNER JOIN my_table ON my_table_2.my_id_2 = my_table.my_id
WHERE field_a = 1234;

另一种方式

SELECT field_b
FROM my_table_2 m2
WHERE EXISTS (
     SELECT my_id FROM my_table 
     WHERE field_a = 1234 and m2.my_id_2=my_table.my_id
);

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这不一定是相同的语义。联接可能会引入重复项。可能尝试使用全名，即

WHERE my_table_2.my_id_2 IN（…）