Subquery returned more than 1 value. This is not permitted when the subquery follows … or when the subquery is used as an expression

Question

I know subquery return more than 1 value but I don't know how to change the code. Can anyone help me?

declare @sProjectNumber nvarchar(200)

( select Project from Project_Table where  Project in (
            select case 
            when @sProject is null then (select distinct Project from Project_Table)
            else @sProject end
from Project_Table)
)

Answer 1

I am guessing that you really intend something like this:

select Project
from Project_Table
where @sProject is NULL or Project = @sProject;

This will return the project in @sProject or all projects if that value is NULL .