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/

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

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random index mysql order-by-rand
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index for better performance for a merge operation

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Join with inequalities only

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inequality join