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Make pg_stats example query result a bit less wide, and add comment about

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pg_stats.inherited
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Alvaro Herrera 2010-04-28 16:48:21 +00:00
parent 9b8a73326e
commit 5f70a04c56
1 changed files with 21 additions and 6 deletions
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27
doc/src/sgml/perform.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.77 2010/04/28 16:10:40 heikki Exp $ --> <!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.78 2010/04/28 16:48:21 alvherre Exp $ -->
<chapter id="performance-tips"> <chapter id="performance-tips">
<title>Performance Tips</title> <title>Performance Tips</title>
@ -554,16 +554,31 @@ WHERE relname LIKE 'tenk1%';
For example, we might do: For example, we might do:
<screen> <screen>
SELECT attname, n_distinct, most_common_vals SELECT attname, inherited, n_distinct,
array_to_string(most_common_vals, E'\n') as most_common_vals
FROM pg_stats FROM pg_stats
WHERE tablename = 'road'; WHERE tablename = 'road';
attname | n_distinct | most_common_vals attname | inherited | n_distinct | most_common_vals
---------+------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------+-----------+------------+------------------------------------
name | -0.467008 | {"I- 580 Ramp","I- 880 Ramp","Sp Railroad ","I- 580 ","I- 680 Ramp","I- 80 Ramp","14th St ","5th St ","Mission Blvd","I- 880 "} name | f | -0.363388 | I- 580 Ramp+
thepath | 20 | {"[(-122.089,37.71),(-122.0886,37.711)]"} | | | I- 880 Ramp+
| | | Sp Railroad +
| | | I- 580 +
| | | I- 680 Ramp
name | t | -0.284859 | I- 880 Ramp+
| | | I- 580 Ramp+
| | | I- 680 Ramp+
| | | I- 580 +
| | | State Hwy 13 Ramp
(2 rows) (2 rows)
</screen> </screen>
Note that two rows are displayed for the same column, one corresponding
to the complete inheritance hierarchy starting at the
<literal>road</literal> table (<literal>inherited</>=<literal>t</>),
and another one including only the <literal>road</literal> table itself
(<literal>inherited</>=<literal>f</>).
</para> </para>
<para> <para>