blob: 7f5711257044a1e655d7e91fb39f0d1bda5a4971 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
|
<refentry id="SQL-EXPLAIN">
<refmeta>
<refentrytitle>
EXPLAIN
</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
EXPLAIN
</refname>
<refpurpose>
Shows statement execution details
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>1998-09-01</date>
</refsynopsisdivinfo>
<synopsis>
EXPLAIN [ VERBOSE ] <replaceable class="PARAMETER">query</replaceable>
</synopsis>
<refsect2 id="R2-SQL-EXPLAIN-1">
<refsect2info>
<date>1998-09-01</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<variablelist>
<varlistentry>
<term>VERBOSE</term>
<listitem>
<para>
Flag to show detailed query plan.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">query</replaceable></term>
<listitem>
<para>
Any <replaceable class="PARAMETER">query</replaceable>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-EXPLAIN-2">
<refsect2info>
<date>1998-04-15</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<varlistentry>
<term><computeroutput>
NOTICE: QUERY PLAN:
<replaceable>plan</replaceable>
</computeroutput></term>
<listitem>
<para>
Explicit query plan from the <productname>Postgres</productname> backend.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><computeroutput>
EXPLAIN
</computeroutput></term>
<listitem>
<para>
Flag sent after query plan is shown.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-SQL-EXPLAIN-1">
<refsect1info>
<date>1998-04-15</date>
</refsect1info>
<title>
Description
</title>
<para>
This command outputs details about the supplied query.
The default output is the computed query cost.
The cost value is only meaningful to the optimizer in comparing
various query plans.
VERBOSE displays the full query plan and cost to your screen,
and pretty-prints the plan to the postmaster log file.
</para>
<refsect2 id="R2-SQL-EXPLAIN-3">
<refsect2info>
<date>1998-04-15</date>
</refsect2info>
<title>
Notes
</title>
<para>
There is only sparse documentation on the optimizer's use of cost
information in <productname>Postgres</productname>.
General information on cost estimation for query optimization
can be found in database textbooks.
Refer to the <citetitle>Programmer's Guide</citetitle>
in the chapters on indexes and the genetic query optimizer for
more information.
</para>
</refsect2>
</refsect1>
<refsect1 id="R1-SQL-EXPLAIN-2">
<title>
Usage
</title>
<para>
To show a query plan for a simple query:
<programlisting>
EXPLAIN select * from foo;
NOTICE: QUERY PLAN:
Seq Scan on foo (cost=0.00 rows=0 width=4)
EXPLAIN
</programlisting>
</para>
</refsect1>
<refsect1 id="R1-SQL-EXPLAIN-3">
<title>
Compatibility
</title>
<para>
</para>
<refsect2 id="R2-SQL-EXPLAIN-4">
<refsect2info>
<date>1998-09-01</date>
</refsect2info>
<title>
SQL92
</title>
<para>
There is no <command>EXPLAIN</command> statement defined in SQL92.
</para>
</refsect2>
</refsect1>
</refentry>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:nil
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
sgml-parent-document:nil
sgml-default-dtd-file:"../reference.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:"/usr/lib/sgml/catalog"
sgml-local-ecat-files:nil
End:
-->
|
