是否可以用不同的值更新表中的多条记录？

Question

我正在使用 SQL，我需要使用以下内容进行多次更新：

UPDATE databaseID SET count = 51 WHERE codCountry = "ES" AND file = "ES_IN.txt"
UPDATE databaseID SET count = 15 WHERE codCountry = "ES" AND file = "ES_DA.txt"
UPDATE databaseID SET count = 84 WHERE codCountry = "CO" AND file = "CO_SE.txt"
UPDATE databaseID SET count = 74 WHERE codCountry = "CO" AND file = "CO_TE.txt"

我的问题是，是否有可能做如下的事情，即在单个查询中更新表的多行？

UPDATE databaseID (SET count = 51 WHERE codCountry = "ES" AND file = "ES_IN.txt"), (SET count = 15 WHERE codCountry = "ES" AND file = "ES_DA.txt")...

Answer 1

我会建议一个派生表和join:

UPDATE databaseID d JOIN
       (SELECT 'ES' as codCountry, 'ES_IN.txt' as file, 15 as count UNION ALL
        SELECT 'CO' as codCountry, 'CO_SE.txt' as file, 51 as count UNION ALL
         . . .
       ) x
       USING (codCountry, file)        
    SET d.count = x.count;

如果原始数据已经在表中，这就更简单了。然后你就可以使用那个表了。

Answer 2

使用CASE 表达式：

UPDATE databaseID 
SET count = CASE 
    WHEN codCountry = 'ES' AND file = 'ES_IN.txt' THEN 51 
    WHEN codCountry = 'ES' AND file = 'ES_DA.txt' THEN 15
    WHEN codCountry = 'CO' AND file = 'CO_SE.txt' THEN 84
    WHEN codCountry = 'CO' AND file = 'CO_TE.txt' THEN 74
    ELSE count
END

如果达到ELSE 部分，MySql 将不会真正更新该行。

或者你可以添加一个WHERE 子句：

UPDATE databaseID 
SET count = CASE 
    WHEN codCountry = 'ES' AND file = 'ES_IN.txt' THEN 51 
    WHEN codCountry = 'ES' AND file = 'ES_DA.txt' THEN 15
    WHEN codCountry = 'CO' AND file = 'CO_SE.txt' THEN 84
    WHEN codCountry = 'CO' AND file = 'CO_TE.txt' THEN 74
END
WHERE (codCountry, file) IN 
  ('ES', 'ES_IN.txt'), ('ES', 'ES_DA.txt'), ('CO', 'CO_SE.txt'), ('CO', 'CO_TE.txt')

并删除CASE 表达式的ELSE 部分。