SQL Server case函数的使用

1: select case A when ' ' then ( case B when ' ' then C else B end ) else A end from table_name

2: select

case

when A <>  ' ' or A is not null then A

when B <>  ' ' or B is not null then B

when C <>  ' ' or C is not null then C 

end

from table_name

从表中首先查询列A的值，当A为空时查询B的值，B为空时查询C的值

ps:新增2 更为严谨