mysql - select the TOP N rows from a table

Question

I am making some paging, and I need to make some query and get the result form defined slicing . for example: I need to get all "top" rows in range 20n < x < 40n etc.

SELECT * FROM Reflow  
WHERE ReflowProcessID = somenumber
ORDER BY ID DESC;

and now I need to make my sliding by column called ID .

Any suggestions how to so ? I need to run my query on mysql, mssql, and oracle.

Answer 1

Assuming your page size is 20 record, and you wanna get page number 2, here is how you would do it:

SQL Server, Oracle:

SELECT *   -- <-- pick any columns here from your table, if you wanna exclude the RowNumber
FROM (SELECT ROW_NUMBER OVER(ORDER BY ID DESC) RowNumber, * 
      FROM Reflow  
      WHERE ReflowProcessID = somenumber) t
WHERE RowNumber >= 20 AND RowNumber <= 40    

MySQL:

SELECT * 
FROM Reflow  
WHERE ReflowProcessID = somenumber
ORDER BY ID DESC
LIMIT 20 OFFSET 20