Databases Reference
In-Depth Information
Optimizing indexes with EXPLAIN
In this section, we want to get some information about the index that MySQL uses
for a specific query, and the performance impact of not having defined an index.
Let us assume we want to use the following query:
SELECT *
FROM `book`
WHERE author_id = 2 AND language = 'es'
We want to know, which topics written by the author whose
id
is
2
, are in the
es
languageāour code for Spanish.
To enter this query, we use the
SQL
tab from the database or the table menu, or the
SQL Query window (refer to
Chapter
11
). We enter this query in the query box and
click
Go
. Whether the query finds any results, is not important right now.
You could obtain the same query by following explanations from
Chapter
8
to produce a search for
author_id
2
and language
es
.
We will now use the
[Explain
SQL]
link to get information about which index
(if any) has been used for this query:
Search WWH ::
Custom Search