Question

For example if I have following statement:

declare @uid int;
set @uid = (select id from tablename where condition)

In this case if the select returns no results, what will the value of @uid be?

Answer 1

in simple words it will be null

I have made simple temporary table to test this

declare @temp table 
 (
   id int identity(1,1) not null  ,
   alpha nvarchar(50)
 )

 insert into @temp select 'z'

declared a variable nvarchar type and get value in this where condition is not meet then there is null and if you see by print statement then there should be nothing will be print

declare @test nvarchar(50)


 select @test=alpha from @temp where id=70

 insert into @temp  select @test 
 select * from @temp


 print @test

I just insert this again to confirm that there is null