如果按分组方式填充了至少一个，则更新列

Question

我正在尝试更新 col_a ，以使其中至少一个用“ > app ”分组，按 col_b

我很难思考该怎么做。

当前情况： 表A

+----+--------------+------+
|id  | col_a        | col_b|
+----+--------------+------+
| 1  | App          | 1111 |
+----+--------------+------+
| 2  | NULL         | 1111 |
+----+--------------+------+
| 3  | NULL         | 1111 |
+----+--------------+------+
| 4  | App          | 1111 |
+----+--------------+------+
| 5  | Tus          | 2222 |
+----+--------------+------+
| 6  | NULL         | 2222 |
+----+--------------+------+
| 7  | Hoe          | 2222 |
+----+--------------+------+
| 8  | NULL         | 2222 |
+----+--------------+------+
| 9  | App          | 3333 |
+----+--------------+------+
| 10 | NULL         | 3333 |
+----+--------------+------+
| 11 | App          | 3333 |
+----+--------------+------+
| 12 | NULL         | 3333 |
+----+--------------+------+

所需结果： 表A

+----+--------------+------+
|id  | col_a        | col_b|
+----+--------------+------+
| 1  | App          | 1111 |
+----+--------------+------+
| 2  | App          | 1111 |
+----+--------------+------+
| 3  | App          | 1111 |
+----+--------------+------+
| 4  | App          | 1111 |
+----+--------------+------+
| 5  | Tus          | 2222 |
+----+--------------+------+
| 6  | NULL         | 2222 |
+----+--------------+------+
| 7  | Hoe          | 2222 |
+----+--------------+------+
| 8  | NULL         | 2222 |
+----+--------------+------+
| 9  | App          | 3333 |
+----+--------------+------+
| 10 | App          | 3333 |
+----+--------------+------+
| 11 | App          | 3333 |
+----+--------------+------+
| 12 | App          | 3333 |
+----+--------------+------+

Answer 1

Infinity

过滤所有update your_table_name set col_a = 'App' where col_b IN (select col_b from your_table_name where col_a = 'App') 值，并仅更新过滤后的值中包含col_b值的那些值。

您可以使用col_b通过这种方式进一步优化它：

is null

#UPDATE：

• 上面的查询引发了一个错误，该错误在 MySQL 中两次被提及。

方法1：

为避免此问题，我们可以创建表名的别名并对其进行调整，如下所示：

update your_table_name
set col_a = 'App'
where col_a IS NULL and col_b IN (select col_b from your_table_name where col_a = 'App')

方法2：

我们可以使用自身对表进行内部联接，并对其中具有update your_table_name set col_a = 'App' where col_a IS NULL and col_b IN (select col_b from (select * from your_table_name) t2 where col_a = 'App') 的{​​{1}}值进行分组，然后相应地更新行。这将提高性能。

col_b