SQL NULL

表

select CHARACTER_MAXIMUM_LENGTH from information_schema.columns where table_name= 'Alliance'

select CHARACTER_MAXIMUM_LENGTH from information_schema.columns where table_name= 'Alliance' and CHARACTER_MAXIMUM_LENGTH is not null;

select CHARACTER_MAXIMUM_LENGTH from information_schema.columns where table_name= 'Alliance' and CHARACTER_MAXIMUM_LENGTH is null;

当遇到Case(字段)..when..then..when.. then..else...end

 select case ISNULL(Cast(CHARACTER_MAXIMUM_LENGTH as varchar()),'')
       when '' then ''
       else '('+Cast(CHARACTER_MAXIMUM_LENGTH as varchar())+')' end as DATA
       from information_schema.columns
where table_name= 'Alliance'

一定要用ISNULL转化过来，不能用when NULL

或者使用

case when field is null then...else..end

select case
 when CHARACTER_MAXIMUM_LENGTH is null then ''
 else '('+Cast(CHARACTER_MAXIMUM_LENGTH as varchar())+')' end as DATA
  from information_schema.columns
where table_name= 'Alliance'