MySQL Example Scripts for “Partial Results”


This section contains the create and insert statements to run the examples from Chapter 7, “Partial Results” in a MySQL database.

Querying Top-N Rows

An indexed Top-N query doesn’t show a “filesort” operation in the Extras column:

SELECT *
  FROM sales
 ORDER BY sale_date DESC
 LIMIT 10;

+----+-------+-------+-------------+--------+-------+
| id | table | type  | key         | rows   | Extra |
+----+-------+-------+-------------+--------+-------+
|  1 | sales | index | sales_dt_pr | 836092 |       | 
+----+-------+-------+-------------+--------+-------+

About the Author

Photo of Markus Winand
Markus Winand tunes developers for high SQL performance. He also published the book SQL Performance Explained and offers in-house training as well as remote coaching at http://winand.at/

?Recent questions at
Ask.Use-The-Index-Luke.com

0
votes
0
answers
700
views

Index for PostgreSQL ORDER BY

Apr 21 at 09:39 Lamplighter 1
postgresql
-1
votes
0
answers
2.1k
views

ORACLE 12C Unstructured Data Management (text mining)

Mar 11 at 09:19 Helraezer 0
oracle unstructured 12c data
1
vote
2
answers
6.1k
views

"Order by RAND()" - can use Index?

Feb 23 at 12:06 Markus Winand ♦♦ 936
random index mysql order-by-rand