How to Select Top 100 rows in Oracle?

My requirement is to get each client’s latest order, and then get top 100 records.

I wrote one query as below to get latest orders for each client. Internal query works fine. But I don’t know how to get first 100 based on the results.

    SELECT * FROM (
      SELECT id, client_id, ROW_NUMBER() OVER(PARTITION BY client_id ORDER BY create_time DESC) rn 
      FROM order
    ) WHERE rn=1

Any ideas? Thanks.

Answer

Assuming that create_time contains the time the order was created, and you want the 100 clients with the latest orders, you can:

• add the create_time in your innermost query
• order the results of your outer query by the create_time desc
• add an outermost query that filters the first 100 rows using ROWNUM

Query:

  SELECT * FROM (
     SELECT * FROM (
        SELECT 
          id, 
          client_id, 
          create_time,
          ROW_NUMBER() OVER(PARTITION BY client_id ORDER BY create_time DESC) rn 
        FROM order
      ) 
      WHERE rn=1
      ORDER BY create_time desc
  ) WHERE rownum <= 100

UPDATE for Oracle 12c

With release 12.1, Oracle introduced “real” Top-N queries. Using the new FETCH FIRST... syntax, you can also use:

  SELECT * FROM (
    SELECT 
      id, 
      client_id, 
      create_time,
      ROW_NUMBER() OVER(PARTITION BY client_id ORDER BY create_time DESC) rn 
    FROM order
  ) 
  WHERE rn = 1
  ORDER BY create_time desc
  FETCH FIRST 100 ROWS ONLY)