SQL中CASE WHEN THEN的使用

在mapper.xml文件中,需要直接给查询的数据直接赋值或者别名显示的时候需要用到 CASE WHEN THEN

select

简单case函数(推荐)

• CASE xxx WHEN ‘x’ THEN ‘x’ WHEN ‘x’ THEN ‘x’ ELSE ‘xx’ END

case搜索函数

• CASE WHEN xxx = ‘x’ THEN ‘x’ WHEN xxx = ‘x’ THEN ‘x’ ELSE ‘xx’ END

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扩展

select case 
  when total > max then 2 
  when total < min then 1 
else 0
end
from ta 

update

UPDATE table SET xxx =(
       CASE 
         WHEN xxx > xx THEN 'xx'
         WHEN xxx > xx THEN 'xx'              
         ELSE 'xx'
         END		 )
WHERE y = 'a';