選擇科拉姆如果已經選擇了其他科拉姆爲空

Question

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

我希望得到一個列的值，其中另一種是空或得到明確一列如果兩者都具有從MySQL值

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; 

這將返回DEV列值，如果它是not null否則返回MUL列值。

Answer 3

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