Databases Reference
In-Depth Information
Let's look at the links:
[Edit] [Explain SQL] [Create PHP Code] [Refresh]
We will now use the
[Explain SQL]
link to get information about which index
(if any) has been used for this query:
We can see that the
EXPLAIN
command has been passed to MySQL, telling us that
the
possible_keys
used is
author_language.
Thus, we know that this index will be
used for this type of query. If this index had not existed, the result would have been
quite different:
Here,
possible_keys
(
NULL
)
and the
type
(
ALL
)
mean that no index would be used
and that all rows would need to be examined to find the desired data. Depending on
the total number of rows, this could have a serious impact on the performance. We
can ascertain the exact impact by examining the query timing that phpMyAdmin
displays on each results page and comparing with or without the index:
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