mysql - 如果已选择的另一列为空，则选择一列

Question

DEV|MUL
xyz|null
null|abc
123|456

我想获取另一列为空的列的值，或者如果两者都有来自mysql的值，则专门获取一列

Answer 1

您可以使用IFNULL

SELECT IFNULL(DEV, MUL) as Col FROM myTable  -- MySql

SELECT ISNULL(DEV, MUL) as Col FROM myTable  -- SQL Server

SELECT NVL(DEV, MUL) as Col FROM myTable  -- Oracle

Answer 2

SELECT IFNULL(DEV, MUL) AS VALUE from table table1; 

DEV如果它是返回列值，这将返回not null列MUL值。

Answer 3

select * from tablename where (columnname is null)
and
select * from tablename where (columnname1 is null) and (columnname2 is null)