SHOW EXPLAIN
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This is a preliminary documentation for SHOW EXPLAIN feature.
The code
The latest code is here:
https://code.launchpad.net/~maria-captains/maria/5.5-show-explain
Differences from EXPLAIN output
In MySQL, there are parts of code where EXPLAIN
execution takes different route from actual query execution. When one runs SHOW EXPLAIN
on a running SELECT
query, it will examine different data structures, and hence the output will be slightly different.
One could argue that output of SHOW EXPLAIN
is the correct one. There will be a motion to switch EXPLAIN
to produce the same output like SHOW EXPLAIN
does.
The list of differences follows:
SHOW EXPLAIN
may produce EXPLAIN lines withno matching row in const table
in theEXTRA
column, WHEREEXPLAIN
would have producedImpossible WHERE ...
:
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL no matching row in const table
- AAA he
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