MySQL查询：根据另一个表中的键检索一些行

Question

我是MySQL的新手，所以我将用一个例子来揭露我的问题...

我有两张桌子：

表1：

+----+-----+-----+-----+-----+
| id | a1  | b1  | c1  | d1  |
+----+-----+-----+-----+-----+
|  1 | ... | ... | ... | ... |
|  2 | ... | ... | ... | ... |
|  3 | ... | ... | ... | ... |
|  4 | ... | ... | ... | ... |
|  5 | ... | ... | ... | ... |
|  6 | ... | ... | ... | ... |
+----+-----+-----+-----+-----+

表2：

+----+-----+-----+-----+---------------+
| id | a2  | b2  | c2  | table1_row_id |
+----+-----+-----+-----+---------------+
|  1 | ... | ... | ... | ...           |
|  2 | ... | ... | ... | 4             |
|  3 | ... | ... | ... | ...           |
+----+-----+-----+-----+---------------+

表2列table1_row_id是table1的关键。

我应该使用哪种查询来检索table2.table1_row_id列中未引用的table1数据？

例如，对于上面的表，查询应返回如下表：

+----+-----+-----+-----+-----+
| id | a1  | b1  | c1  | d1  |
+----+-----+-----+-----+-----+
|  1 | ... | ... | ... | ... |
|  2 | ... | ... | ... | ... |
|  3 | ... | ... | ... | ... |
|  5 | ... | ... | ... | ... |
|  6 | ... | ... | ... | ... |
+----+-----+-----+-----+-----+

可能这很简单，但我不知道该怎么办......

Answer 1

SELECT * 
FROM t1 
WHERE 
    `id` NOT IN (SELECT `table1_row_id` 
                 FROM t2 
                 WHERE
                     `table1_row_id` IS NOT NULL)

Answer 2

select t1.a1, t1.b1, t1.c1, t1.d1
from table1 t1
left join table2 t2 on t2.table1_row_id = t1.id
where t2.id is null