UNION

[sardinka2]

I have set of Union statements.I need to validate param if param='123'
then do one more union if not end of select.
When I ran the sp it gives me an error in the union in if statement.
What am I doing incorrect?
Select 1,2,3 from table1
UNION
Select 1,2,3 from table2
...
If @param='123'
Begin
Union
Select 1,2,3 from table3
END

 

[checkai]

Could use dynamic SQL

declare @i as int
declare @str as varchar(8000)
set @i = 2

set @str = 'select 34 as i'

if @i = 2
begin
set @str = @str +' union select 45 as i'
end

exec(@str)

 

[RileyCat]

You could also do something like so ...

select

Union

select

Union

select * from sometable where @parm = truevalue

The third union will only have a return data set if the conditional expression (where @parm = truevalue) resolves to true. Otherwise, nothing will get returned in the last select.

Save the hassle of trying to parse dynamic sql strings.