Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commitd79f2d4

Browse files
committed
Remove IN/slow FAQ item because it only applies to <=7.3.X.
1 parentbfc5362 commitd79f2d4

File tree

2 files changed

+22
-70
lines changed

2 files changed

+22
-70
lines changed

‎doc/FAQ

Lines changed: 11 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,7 @@
11

22
Frequently Asked Questions (FAQ) for PostgreSQL
33

4-
Last updated: Sat Jan 29 23:15:42 EST 2005
4+
Last updated: Sat Jan 29 23:20:03 EST 2005
55

66
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
77

@@ -76,13 +76,12 @@
7676
4.16) Why does my large-object operations get "invalid large obj
7777
descriptor"?
7878
4.17) How do I create a column that will default to the current time?
79-
4.18) Why are my subqueries using IN so slow?
80-
4.19) How do I perform an outer join?
81-
4.20) How do I perform queries using multiple databases?
82-
4.21) How do I return multiple rows or columns from a function?
83-
4.22) Why can't I reliably create/drop temporary tables in PL/PgSQL
79+
4.18) How do I perform an outer join?
80+
4.19) How do I perform queries using multiple databases?
81+
4.20) How do I return multiple rows or columns from a function?
82+
4.21) Why can't I reliably create/drop temporary tables in PL/PgSQL
8483
functions?
85-
4.23) What encryption options are available?
84+
4.22) What encryption options are available?
8685

8786
Extending PostgreSQL
8887

@@ -922,28 +921,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
922921
Use CURRENT_TIMESTAMP:
923922
CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
924923

925-
4.18) Why are my subqueries using IN so slow?
926-
927-
In versions prior to 7.4, subqueries were joined to outer queries by
928-
sequentially scanning the result of the subquery for each row of the
929-
outer query. If the subquery returns only a few rows and the outer
930-
query returns many rows, IN is fastest. To speed up other queries,
931-
replace IN with EXISTS:
932-
SELECT *
933-
FROM tab
934-
WHERE col IN (SELECT subcol FROM subtab);
935-
936-
to:
937-
SELECT *
938-
FROM tab
939-
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
940-
941-
For this to be fast, subcol should be an indexed column.
942-
943-
In version 7.4 and later, IN actually uses the same sophisticated join
944-
techniques as normal queries, and is prefered to using EXISTS.
945-
946-
4.19) How do I perform an outer join?
924+
4.18) How do I perform an outer join?
947925

948926
PostgreSQL supports outer joins using the SQL standard syntax. Here
949927
are two examples:
@@ -973,7 +951,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
973951
WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
974952
ORDER BY col1
975953

976-
4.20) How do I perform queries using multiple databases?
954+
4.19) How do I perform queries using multiple databases?
977955

978956
There is no way to query a database other than the current one.
979957
Because PostgreSQL loads database-specific system catalogs, it is
@@ -983,12 +961,12 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
983961
course, a client can make simultaneous connections to different
984962
databases and merge the results on the client side.
985963

986-
4.21) How do I return multiple rows or columns from a function?
964+
4.20) How do I return multiple rows or columns from a function?
987965

988966
In 7.3, you can easily return multiple rows or columns from a
989967
function, http://techdocs.postgresql.org/guides/SetReturningFunctions.
990968

991-
4.22) Why can't I reliably create/drop temporary tables in PL/PgSQL
969+
4.21) Why can't I reliably create/drop temporary tables in PL/PgSQL
992970
functions?
993971

994972
PL/PgSQL caches function contents, and an unfortunate side effect is
@@ -999,7 +977,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
999977
table access in PL/PgSQL. This will cause the query to be reparsed
1000978
every time.
1001979

1002-
4.23) What encryption options are available?
980+
4.22) What encryption options are available?
1003981

1004982
* contrib/pgcrypto contains many encryption functions for use in SQL
1005983
queries.

‎doc/src/FAQ/FAQ.html

Lines changed: 11 additions & 37 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
alink="#0000ff">
1111
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
1212

13-
<P>Last updated: Sat Jan 29 23:15:42 EST 2005</P>
13+
<P>Last updated: Sat Jan 29 23:20:03 EST 2005</P>
1414

1515
<P>Current maintainer: Bruce Momjian (<Ahref=
1616
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@@ -114,16 +114,14 @@ <H2 align="center">Operational Questions</H2>
114114
<I>"invalid large obj descriptor"</I>?<BR>
115115
<Ahref="#4.17">4.17</A>) How do I create a column that will
116116
default to the current time?<BR>
117-
<Ahref="#4.18">4.18</A>) Why are my subqueries using
118-
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
119-
<Ahref="#4.19">4.19</A>) How do I perform an outer join?<BR>
120-
<Ahref="#4.20">4.20</A>) How do I perform queries using multiple
117+
<Ahref="#4.18">4.18</A>) How do I perform an outer join?<BR>
118+
<Ahref="#4.19">4.19</A>) How do I perform queries using multiple
121119
databases?<BR>
122-
<Ahref="#4.21">4.21</A>) How do I return multiple rows or columns
120+
<Ahref="#4.20">4.20</A>) How do I return multiple rows or columns
123121
from a function?<BR>
124-
<Ahref="#4.22">4.22</A>) Why can't I reliably create/drop
122+
<Ahref="#4.21">4.21</A>) Why can't I reliably create/drop
125123
temporary tables in PL/PgSQL functions?<BR>
126-
<Ahref="#4.23">4.23</A>) What encryption options are available?<BR>
124+
<Ahref="#4.22">4.22</A>) What encryption options are available?<BR>
127125

128126

129127
<H2align="center">Extending PostgreSQL</H2>
@@ -1155,31 +1153,7 @@ <H4><A name="4.17">4.17</A>) How do I create a column that will
11551153
</CODE>
11561154
</PRE>
11571155

1158-
<H4><Aname="4.18">4.18</A>) Why are my subqueries using
1159-
<CODE><SMALL>IN</SMALL></CODE> so slow?</H4>
1160-
1161-
<P>In versions prior to 7.4, subqueries were joined to outer queries
1162-
by sequentially scanning the result of the subquery for each row of
1163-
the outer query. If the subquery returns only a few rows and the outer
1164-
query returns many rows,<CODE><SMALL>IN</SMALL></CODE> is fastest. To
1165-
speed up other queries, replace<CODE>IN</CODE> with
1166-
<CODE>EXISTS</CODE>:</P>
1167-
<PRE> SELECT *
1168-
FROM tab
1169-
WHERE col IN (SELECT subcol FROM subtab);
1170-
</PRE>
1171-
to:
1172-
<PRE> SELECT *
1173-
FROM tab
1174-
WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col);
1175-
</PRE>
1176-
1177-
For this to be fast,<CODE>subcol</CODE> should be an indexed column.
1178-
<P>In version 7.4 and later,<CODE>IN</CODE> actually uses the same
1179-
sophisticated join techniques as normal queries, and is prefered
1180-
to using<CODE>EXISTS</CODE>.
1181-
1182-
<H4><Aname="4.19">4.19</A>) How do I perform an outer join?</H4>
1156+
<H4><Aname="4.18">4.18</A>) How do I perform an outer join?</H4>
11831157

11841158
<P>PostgreSQL supports outer joins using the SQL standard syntax.
11851159
Here are two examples:</P>
@@ -1219,7 +1193,7 @@ <H4><A name="4.19">4.19</A>) How do I perform an outer join?</H4>
12191193
ORDER BY col1
12201194
</PRE>
12211195

1222-
<H4><Aname="4.20">4.20</A>) How do I perform queries using
1196+
<H4><Aname="4.19">4.19</A>) How do I perform queries using
12231197
multiple databases?</H4>
12241198

12251199
<P>There is no way to query a database other than the current one.
@@ -1231,15 +1205,15 @@ <H4><A name="4.20">4.20</A>) How do I perform queries using
12311205
connections to different databases and merge the results on the
12321206
client side.</P>
12331207

1234-
<H4><Aname="4.21">4.21</A>) How do I return multiple rows or
1208+
<H4><Aname="4.20">4.20</A>) How do I return multiple rows or
12351209
columns from a function?</H4>
12361210

12371211
<P>In 7.3, you can easily return multiple rows or columns from a
12381212
function,
12391213
<ahref="http://techdocs.postgresql.org/guides/SetReturningFunctions">
12401214
http://techdocs.postgresql.org/guides/SetReturningFunctions</a>.
12411215

1242-
<H4><Aname="4.22">4.22</A>) Why can't I reliably create/drop
1216+
<H4><Aname="4.21">4.21</A>) Why can't I reliably create/drop
12431217
temporary tables in PL/PgSQL functions?</H4>
12441218
<P>PL/PgSQL caches function contents, and an unfortunate side effect
12451219
is that if a PL/PgSQL function accesses a temporary table, and that
@@ -1249,7 +1223,7 @@ <H4><A name="4.22">4.22</A>) Why can't I reliably create/drop
12491223
<SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This
12501224
will cause the query to be reparsed every time.</P>
12511225

1252-
<H4><Aname="4.23">4.23</A>) What encryption options are available?
1226+
<H4><Aname="4.22">4.22</A>) What encryption options are available?
12531227
</H4>
12541228
<UL>
12551229
<LI><I>contrib/pgcrypto</I> contains many encryption functions for

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp