Question

In Asp.net, I am trying to achieve pagination using following code:

String query="SELECT * "+
             "FROM (SELECT Distinct emp_name, emp_address, "+
             "         ROW_NUMBER() OVER(ORDER BY emp_id) AS rownum"+
             "       FROM Employee"+
             "     )as Person "+
             "WHERE rownum>"+ start +" and rownum <="+ end +";

SqlCommand cmd = new SqlCommand(query, conn);
conn.Open();

SqlDataReader reader = cmd.ExecuteReader();

Above code does not retrieve Distinct rows.
How can I adjust my query to get distinct emp_name and order by emp_id along with total number of entries in single ExecuteReader()?

Currently I am calling ExecuteReader() twice first for data and and second for total count.

I followed SQL Server DISTINCT pagination with ROW_NUMBER() not distinct but was unable to understand how to implement it in my code. Please help.

Answer 1

Use String.Format and raw string (@) to avoid concatenation.

String query = String.Format(@"
    select emp_name, emp_address, rownum 
    from (
        select
            emp_name, emp_address,
            row_number() over(order by emp_id) as rownum
        from (
            select distinct emp_name, emp_address
            from employee
        ) s
    ) as Person 
    where rownum > {0} and rownum <= {1}
    ;
    select count(*) as total
    from (
        select distinct emp_name, emp_address
        from employee
        where rownum > {0} and rownum <= {1}
    ) s
    ;    
", start, end);

SqlCommand cmd = new SqlCommand(query, conn);
conn.Open();

SqlDataReader reader = cmd.ExecuteReader();

// gets the first data set
while (reader.Read())
{
    ...
}

// gets the second
reader.NextResult();
reader.Read();
int total = (int)reader["total"];

Use NextResult to read multiple result sets.