MySql 特殊语法ifnull

1.ifnull(col2=0,'xxx') 

col2 is null 则返回 'xxx' 

col2 is not null 则返回 1

2.ifnull(col2=1,'xxx') 

col2 is null 则返回 'xxx' 

col2 is not null 则返回 0

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1.=0时

select ifnull(null=0,'xxx');    输出 'xxx'

select ifnull('aaa'=0,'xxx');    输出 1

2.=1时

select ifnull(null=1,'xxx');   输出 'xxx'

select ifnull('aaa'=1,'xxx'); 输出 0