Question

Here is what I have so far. I want to store the query result into an int variable but I get null so far. After execute, both @query and @countrow are both null. Any suggestion would be great.

    SET @query = N'select @countrow=count(*) from ' + @tablename 
EXECUTE sp_executesql @query

Answer 1

DECLARE @i INT, @sql NVARCHAR(512), @tablename varchar(200) = 'tbl'

SET @sql = N'SELECT @i = COUNT(*) FROM '  + @tablename

EXEC sp_executesql 
    @query = @sql, 
    @params = N'@i INT OUTPUT', 
    @i = @i OUTPUT 

PRINT @i 

Take a look at SQL Fiddle