mysql what is the right syntax for this conditional update statement

问题

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

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

回答1:

It should be written this way:

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'); 

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.

来源：https://stackoverflow.com/questions/15740557/mysql-what-is-the-right-syntax-for-this-conditional-update-statement