Question

我有一张桌子states_risk：

id | state | municipally | rating

示例：

id | state | municipally | rating 
 1     AG     AG1            5
 2     AG     AG2            6
 3     AG     AG3            2
 4     AG     AG4            1
 5     AG     OTHER          -
 6     AB     AB1            0.2
 7     AB     AB2            2
 8     AB     AB3            10
 9     AB     OTHER          -

我需要更新municipally = OTHER的值“ rating”，并通过状态“ AG”-“ AB”设置MAX(rating)的值，例如：id 5设置一个6值，因为是max AG的价值。

Answer 1

这为您提供了最大值

 SELECT state, max(rating) as maxrating
 FROM states_risk
 GROUP BY state

这为您提供了要更新的内容

 SELECT id, state
 FROM states_risk
 WHERE municiplally = 'OTHER'

所以更新是

 UPDATE states_risk
 SET rating = (
   SELECT max(rating) as maxrating
   FROM states_risk inner
   WHERE inner.state = states_risk.state
 )
 WHERE municiplally = 'OTHER'

Answer 2

您可以通过将表联接到返回每个州的最高评分的查询来做到这一点：

update states_risk s inner join (
  select state, max(rating) rating
  from states_risk
  group by state
) g on g.state = s.state
set s.rating = g.rating
where s.municipally = 'OTHER';

请参见demo。
结果：

| id  | state | municipally | rating |
| --- | ----- | ----------- | ------ |
| 1   | AG    | AG1         | 5      |
| 2   | AG    | AG2         | 6      |
| 3   | AG    | AG3         | 2      |
| 4   | AG    | AG4         | 1      |
| 5   | AG    | OTHER       | 6      |
| 6   | AB    | AB1         | 0.2    |
| 7   | AB    | AB2         | 2      |
| 8   | AB    | AB3         | 10     |
| 9   | AB    | OTHER       | 10     |

Answer 3

如果您的列等级在其列中具有“-”。您还需要铸造柱子喜欢

select version();

| version() |
| :-------- |
| 8.0.18    |

CREATE TABLE states_risk
    (`id` int, `state` varchar(2), `municipally` varchar(5), `rating` varchar(3))
;
INSERT INTO states_risk
    (`id`, `state`, `municipally`, `rating`)
VALUES
    (1, 'AG', 'AG1', '5'),
    (2, 'AG', 'AG2', '6'),
    (3, 'AG', 'AG3', '2'),
    (4, 'AG', 'AG4', '1'),
    (5, 'AG', 'OTHER', '-'),
    (6, 'AB', 'AB1', '0.2'),
    (7, 'AB', 'AB2', '2'),
    (8, 'AB', 'AB3', '10'),
    (9, 'AB', 'OTHER', '-')
;

✓

✓

Select * From states_risk;

id | state | municipally | rating
-: | :---- | :---------- | :-----
 1 | AG    | AG1         | 5     
 2 | AG    | AG2         | 6     
 3 | AG    | AG3         | 2     
 4 | AG    | AG4         | 1     
 5 | AG    | OTHER       | -     
 6 | AB    | AB1         | 0.2   
 7 | AB    | AB2         | 2     
 8 | AB    | AB3         | 10    
 9 | AB    | OTHER       | -

SELECT state, MAX(CAST(rating as FLOAT)) MAXrating 
                              FROM states_risk WHERE rating <> '-' GROUP BY state

state | MAXrating
:---- | --------:
AG    |         6
AB    |        10

UPDATE states_risk sr INNER JOIN (SELECT state, MAX(CAST(rating as FLOAT)) MAXrating 
                              FROM states_risk WHERE rating <> '-' GROUP BY state) t1 
                              ON sr.state = t1.state
SET sr.rating = t1.MAXrating WHERE sr.municipally = 'OTHER';

✓

Select * From states_risk;

id | state | municipally | rating
-: | :---- | :---------- | :-----
 1 | AG    | AG1         | 5     
 2 | AG    | AG2         | 6     
 3 | AG    | AG3         | 2     
 4 | AG    | AG4         | 1     
 5 | AG    | OTHER       | 6     
 6 | AB    | AB1         | 0.2   
 7 | AB    | AB2         | 2     
 8 | AB    | AB3         | 10    
 9 | AB    | OTHER       | 10

db <>提琴here

用另一列最大值更新

3 个答案: