根据另一列的更改来更改一列的值

Question

假设我有一个这样的SQL表：

+----+------+-------+
| id | ColA | ColB  |
+----+------+-------+
|  1 | red  | false |
+----+------+-------+

当我将colB的值设置为'true'时，我希望colA的值更改为'blue'，所以我最终得到：

+----+------+------+
| id | ColA | ColB |
+----+------+------+
|  1 | blue | true |
+----+------+------+

我意识到我可以同时更新两个列，但是我想知道是否可以在数据库中添加自动执行此操作的规则。

我正在使用psql 10.4。

Answer 1

只是用例，因为您没有提到任何逻辑，所以假设您要用红色，然后用蓝色和真

select id, case when ColA='red' then 'blue' end as ColA,
case when ColA='red' then true end as ColB from t

Answer 2

Since Postgresql 10 does not support computed columns, I think you have three options:

1. Define a trigger that updates ColA when ColB is updated.

2. Define a view on top of original table that computes ColA.

3. Forget having ColA in database and compute the value in SELECT.