我知道你可以一次插入多行，是否有一种方法可以一次更新多行(如在，在一个查询)在MySQL?
编辑: 例如，我有以下内容
Name id Col1 Col2
Row1 1 6 1
Row2 2 2 3
Row3 3 9 5
Row4 4 16 8
我想将以下所有更新组合成一个查询
UPDATE table SET Col1 = 1 WHERE id = 1;
UPDATE table SET Col1 = 2 WHERE id = 2;
UPDATE table SET Col2 = 3 WHERE id = 3;
UPDATE table SET Col1 = 10 WHERE id = 4;
UPDATE table SET Col2 = 12 WHERE id = 4;
当前回答
下面是简单的方法
update my_table m, -- let create a temp table with populated values
(select 1 as id, 20 as value union -- this part will be generated
select 2 as id, 30 as value union -- using a backend code
-- for loop
select N as id, X as value
) t
set m.value = t.value where t.id=m.id -- now update by join - quick
其他回答
不知道为什么没有提到另一个有用的选项:
UPDATE my_table m
JOIN (
SELECT 1 as id, 10 as _col1, 20 as _col2
UNION ALL
SELECT 2, 5, 10
UNION ALL
SELECT 3, 15, 30
) vals ON m.id = vals.id
SET col1 = _col1, col2 = _col2;
这个问题很老了，但我想用另一个答案来扩展这个话题。
我的观点是，实现它的最简单的方法是用一个事务包装多个查询。这句话的意思是:ON DUPLICATE KEY UPDATE是一个很好的黑客，但人们应该意识到它的缺点和限制:
As being said, if you happen to launch the query with rows whose primary keys don't exist in the table, the query inserts new "half-baked" records. Probably it's not what you want If you have a table with a not null field without default value and don't want to touch this field in the query, you'll get "Field 'fieldname' doesn't have a default value" MySQL warning even if you don't insert a single row at all. It will get you into trouble, if you decide to be strict and turn mysql warnings into runtime exceptions in your app.
I made some performance tests for three of suggested variants, including the INSERT ... ON DUPLICATE KEY UPDATE variant, a variant with "case / when / then" clause and a naive approach with transaction. You may get the python code and results here. The overall conclusion is that the variant with case statement turns out to be twice as fast as two other variants, but it's quite hard to write correct and injection-safe code for it, so I personally stick to the simplest approach: using transactions.
编辑:Dakusan的发现证明我的性能估计不太有效。请参阅另一个更详细的研究的答案。
use
REPLACE INTO`table` VALUES (`id`,`col1`,`col2`) VALUES
(1,6,1),(2,2,3),(3,9,5),(4,16,8);
请注意:
Id必须是一个主唯一键 如果使用外键来 引用表，REPLACE删除然后插入，所以这可能 造成错误
下面是简单的方法
update my_table m, -- let create a temp table with populated values
(select 1 as id, 20 as value union -- this part will be generated
select 2 as id, 30 as value union -- using a backend code
-- for loop
select N as id, X as value
) t
set m.value = t.value where t.id=m.id -- now update by join - quick
由于您有动态值，因此需要为要更新的列使用IF或CASE。虽然有点难看，但应该能行。
用你的例子，你可以这样做:
UPDATE table SET Col1 = CASE id
WHEN 1 THEN 1
WHEN 2 THEN 2
WHEN 4 THEN 10
ELSE Col1
END,
Col2 = CASE id
WHEN 3 THEN 3
WHEN 4 THEN 12
ELSE Col2
END
WHERE id IN (1, 2, 3, 4);
