SQLServer 中判斷字段、變量是否爲NULL或空字符

一、字段判斷

（1）是否爲空

select * from department where leader is NULL
select * from department where leader is not NULL

（2）是否爲空字符‘’

select * from department where leader=''

select * from department where leader!=''
select * from department where leader<>''

 

二、變量判斷

（1）是否爲空

declare @r varchar(50)='abc'
	if @r is null
	begin
	  set @r='暫無數據'
	end 
	else if @r is not null
	begin
	  set @r='數據爲：'+ @r
	end
select @r

------------- begin 和 end 不寫也是闊以的，就是寫上會顯得規範些---------------

declare @r varchar(50)=NULL
	if @r is null
	  set @r='暫無數據'
	else if @r is not null
	  set @r='數據爲：'+ @r
select @r

（2）是否爲空字符‘’

declare @r varchar(50)='324'
	if @r = ''
	  set @r='暫無數據'
	else if @r != ''
	  set @r='數據爲：'+ @r
select @r

--------------------------------

declare @r varchar(50)='bbb'
	if LEN(@r) = 0
	  set @r='暫無數據'
	else if LEN(@r) != 0
	  set @r='數據爲：'+ @r
select @r