mysql此条件更新语句的正确语法是什么 [英] mysql what is the right syntax for this conditional update statement

问题描述

MYSQL，我想要的是

MYSQL, what I want is like

update tablename 

case fieldA

when value1 then set fieldX0=xxx,fieldX1=bbb,fieldX2=ccc ...

when value2 then set fieldY0=yyy,fieldY1=eee,fieldY2=fff ...

end

什么是正确且简单的语法?非常感谢.

what is the right and simple syntax for it? thank you very much.

推荐答案

应该这样写:

UPDATE tablename
SET fieldX = CASE WHEN fieldA = 'value1' THEN 'xxx' ELSE fieldX END,
    fieldY = CASE WHEN fieldA = 'value2' THEN 'yyy' ELSE fieldY END
WHERE fieldA IN ('value1', 'value2'); 

请注意:我这样写ELSE部分，因为如果CASE表达式的条件无效，则ELSE的默认值为NULL.会将其设置为原始值，而不是NULL值.

Note that: I wrote the ELSE part this way, because the default for the ELSE is NULL if the condition of the CASE expression is not valid, so this will set it to the original value not to the NULL value.

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