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Commit 061168d

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tglsfdctglsfdc
committed
Code review for FETCH/MOVE 0 changes. Improve documentation, do the
right thing with the destination when FETCH 0 can't return a row, don't try to stuff LONG_MAX into an int value.
1 parent 1bc9e98 commit 061168d

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-74
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5 files changed

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‎doc/src/sgml/ref/fetch.sgml

Lines changed: 49 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$Header: /cvsroot/pgsql/doc/src/sgml/ref/fetch.sgml,v 1.22 2002/12/30 15:31:47 momjian Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/ref/fetch.sgml,v 1.23 2003/01/08 00:22:26 tgl Exp $
33
PostgreSQL documentation
44
-->
55

@@ -22,7 +22,7 @@ PostgreSQL documentation
2222
</refsynopsisdivinfo>
2323
<synopsis>
2424
FETCH [ <replaceable class="PARAMETER">direction</replaceable> ] [ <replaceable class="PARAMETER">count</replaceable> ] { IN | FROM } <replaceable class="PARAMETER">cursor</replaceable>
25-
FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</replaceable> | ALL | NEXT | PRIOR ]
25+
FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</replaceable> | ALL | LAST | NEXT | PRIOR ]
2626
{ IN | FROM } <replaceable class="PARAMETER">cursor</replaceable>
2727
</synopsis>
2828

@@ -40,7 +40,7 @@ FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</repl
4040
<term><replaceable class="PARAMETER">direction</replaceable></term>
4141
<listitem>
4242
<para>
43-
<replaceable class="PARAMETER">selector</replaceable>
43+
<replaceable class="PARAMETER">direction</replaceable>
4444
defines the fetch direction. It can be one of
4545
the following:
4646

@@ -50,7 +50,7 @@ FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</repl
5050
<listitem>
5151
<para>
5252
fetch next row(s). This is the default
53-
if <replaceable class="PARAMETER">selector</replaceable> is omitted.
53+
if <replaceable class="PARAMETER">direction</replaceable> is omitted.
5454
</para>
5555
</listitem>
5656
</varlistentry>
@@ -87,9 +87,9 @@ FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</repl
8787
<term><replaceable class="PARAMETER">#</replaceable></term>
8888
<listitem>
8989
<para>
90-
A signed integer that specifies how many rows to fetch.
90+
A signed integer constant that specifies how many rows to fetch.
9191
Note that a negative integer is equivalent to changing the sense of
92-
FORWARD and BACKWARD. Zero re-fetches the current row.
92+
FORWARD and BACKWARD. Zero re-fetches the current row, if any.
9393
</para>
9494
</listitem>
9595
</varlistentry>
@@ -105,6 +105,17 @@ FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</repl
105105
</listitem>
106106
</varlistentry>
107107

108+
<varlistentry>
109+
<term>
110+
LAST
111+
</term>
112+
<listitem>
113+
<para>
114+
Same as <literal>ALL</>, but conforms to SQL92 syntax.
115+
</para>
116+
</listitem>
117+
</varlistentry>
118+
108119
<varlistentry>
109120
<term>
110121
NEXT
@@ -151,7 +162,8 @@ FETCH [ FORWARD | BACKWARD | RELATIVE ] [ <replaceable class="PARAMETER">#</repl
151162
Outputs
152163
</title>
153164
<para>
154-
<command>FETCH</command> returns the results of the query defined by the specified cursor.
165+
<command>FETCH</command> returns rows from the result of the query defined
166+
by the specified cursor.
155167
The following messages will be returned if the query fails:
156168

157169
<variablelist>
@@ -200,10 +212,33 @@ WARNING: FETCH/ABSOLUTE not supported, using RELATIVE
200212
If the number of rows remaining in the cursor is less
201213
than <replaceable class="PARAMETER">#</replaceable>,
202214
then only those available are fetched.
203-
Substituting the keyword ALL in place of a number will
215+
Substituting the keyword ALL or LAST in place of a number will
204216
cause all remaining rows in the cursor to be retrieved.
205-
Instances may be fetched in both FORWARD and BACKWARD
217+
Rows may be fetched in both FORWARD and BACKWARD
206218
directions. The default direction is FORWARD.
219+
</para>
220+
221+
<para>
222+
The cursor position can be before the first row of the query result, or on
223+
any particular row of the result, or after the last row of the result.
224+
When created, a cursor is positioned before the first row. After fetching
225+
some rows, the cursor is positioned on the last row retrieved. A new
226+
<command>FETCH</command> always steps one row in the specified direction
227+
(if possible) before beginning to return rows. If the
228+
<command>FETCH</command> requests more rows than available, the cursor is
229+
left positioned after the last row of the query result (or before the first
230+
row, in the case of a backward fetch). This will always be the case after
231+
<command>FETCH ALL</>.
232+
</para>
233+
234+
<tip>
235+
<para>
236+
A zero row count requests fetching the current row without moving the
237+
cursor --- that is, re-fetching the most recently fetched row.
238+
This will succeed unless the cursor is positioned before the
239+
first row or after the last row; in which case, no row is returned.
240+
</para>
241+
</tip>
207242

208243
<tip>
209244
<para>
@@ -213,7 +248,6 @@ WARNING: FETCH/ABSOLUTE not supported, using RELATIVE
213248
<command>FORWARD -1</command> is the same as <command>BACKWARD 1</command>.
214249
</para>
215250
</tip>
216-
</para>
217251

218252
<refsect2 id="R2-SQL-FETCH-3">
219253
<refsect2info>
@@ -224,11 +258,9 @@ WARNING: FETCH/ABSOLUTE not supported, using RELATIVE
224258
</title>
225259

226260
<para>
227-
Note that the FORWARD and BACKWARD keywords are
261+
Note that the FORWARD, BACKWARD, and ALL keywords are
228262
<productname>PostgreSQL</productname> extensions.
229-
The <acronym>SQL92</acronym> syntax is also supported, specified
230-
in the second form of the command. See below for details
231-
on compatibility issues.
263+
See below for details on compatibility issues.
232264
</para>
233265

234266
<para>
@@ -246,11 +278,11 @@ WARNING: FETCH/ABSOLUTE not supported, using RELATIVE
246278
</para>
247279

248280
<para>
281+
<xref linkend="sql-declare" endterm="sql-declare-title">
282+
is used to define a cursor.
249283
Use
250284
<xref linkend="sql-move" endterm="sql-move-title">
251-
to change cursor position.
252-
<xref linkend="sql-declare" endterm="sql-declare-title">
253-
will define a cursor.
285+
to change cursor position without retrieving data.
254286
Refer to
255287
<xref linkend="sql-begin" endterm="sql-begin-title">,
256288
<xref linkend="sql-commit" endterm="sql-commit-title">,

‎doc/src/sgml/ref/move.sgml

Lines changed: 7 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$Header: /cvsroot/pgsql/doc/src/sgml/ref/move.sgml,v 1.15 2002/12/30 15:31:47 momjian Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/ref/move.sgml,v 1.16 2003/01/08 00:22:26 tgl Exp $
33
PostgreSQL documentation
44
-->
55

@@ -13,17 +13,15 @@ PostgreSQL documentation
1313
MOVE
1414
</refname>
1515
<refpurpose>
16-
position a cursor on a specified row of a table
16+
reposition a cursor
1717
</refpurpose>
1818
</refnamediv>
1919
<refsynopsisdiv>
2020
<refsynopsisdivinfo>
2121
<date>1999-07-20</date>
2222
</refsynopsisdivinfo>
2323
<synopsis>
24-
MOVE [ <replaceable class="PARAMETER">direction</replaceable> ]
25-
{<replaceable class="PARAMETER">count</replaceable> | LAST }
26-
{ IN | FROM } <replaceable class="PARAMETER">cursor</replaceable>
24+
MOVE [ <replaceable class="PARAMETER">direction</replaceable> ] [ <replaceable class="PARAMETER">count</replaceable> ] { IN | FROM } <replaceable class="PARAMETER">cursor</replaceable>
2725
</synopsis>
2826
</refsynopsisdiv>
2927

@@ -35,12 +33,10 @@ MOVE [ <replaceable class="PARAMETER">direction</replaceable> ]
3533
Description
3634
</title>
3735
<para>
38-
<command>MOVE</command> allows a user to move the cursor position a
39-
specified number of rows.
40-
<command>MOVE</command> works like the <command>FETCH</command> command,
41-
but only positions the cursor and does not return rows.
42-
<replaceable class="PARAMETER">LAST</replaceable> moves to the end
43-
of the cursor.
36+
<command>MOVE</command> allows the user to move the cursor position a
37+
specified number of rows, or all the way to the end or start of the query.
38+
<command>MOVE</command> works exactly like the <command>FETCH</command>
39+
command, except it only repositions the cursor and does not return rows.
4440
</para>
4541
<para>
4642
Refer to

‎doc/src/sgml/release.sgml

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.175 2003/01/06 18:53:23 petere Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/release.sgml,v 1.176 2003/01/08 00:22:26 tgl Exp $
33
-->
44

55
<appendix id="release">
@@ -24,6 +24,7 @@ CDATA means the content is "SGML-free", so you can write without
2424
worries about funny characters.
2525
-->
2626
<literallayout><![CDATA[
27+
FETCH 0 now re-fetches cursor's current row, per SQL spec
2728
Revised executor state representation; plan trees are read-only to executor now
2829
Information schema
2930
Domains now support CHECK constraints

‎src/backend/commands/portalcmds.c

Lines changed: 49 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/commands/portalcmds.c,v 1.7 2002/12/30 15:31:47 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/commands/portalcmds.c,v 1.8 2003/01/08 00:22:27 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -55,7 +55,7 @@ PortalCleanup(Portal portal)
5555
*
5656
* name: name of portal
5757
* forward: forward or backward fetch?
58-
* count: # of tuples to fetch
58+
* count: # of tuples to fetch (INT_MAX means "all"; 0 means "refetch")
5959
* dest: where to send results
6060
* completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE
6161
* in which to store a command completion status string.
@@ -100,18 +100,15 @@ PerformPortalFetch(char *name,
100100
return;
101101
}
102102

103-
/* If zero count, handle specially */
103+
/*
104+
* Zero count means to re-fetch the current row, if any (per SQL92)
105+
*/
104106
if (count == 0)
105107
{
106-
bool on_row = false;
108+
bool on_row;
107109

108110
/* Are we sitting on a row? */
109-
oldcontext = MemoryContextSwitchTo(PortalGetHeapMemory(portal));
110-
queryDesc = PortalGetQueryDesc(portal);
111-
estate = queryDesc->estate;
112-
if (portal->atStart == false && portal->atEnd == false)
113-
on_row = true;
114-
MemoryContextSwitchTo(oldcontext);
111+
on_row = (portal->atStart == false && portal->atEnd == false);
115112

116113
if (dest == None)
117114
{
@@ -122,26 +119,25 @@ PerformPortalFetch(char *name,
122119
}
123120
else
124121
{
125-
/* If we are not on a row, FETCH 0 returns nothing */
126-
if (!on_row)
127-
return;
128-
129-
/* Since we are sitting on a row, return the row */
130-
/* Back up so we can reread the row */
131-
PerformPortalFetch(name, false /* backward */, 1,
132-
None, /* throw away output */
133-
NULL /* do not modify the command tag */);
134-
135-
/* Set up to fetch one row */
136-
count = 1;
137-
forward = true;
122+
/*
123+
* If we are sitting on a row, back up one so we can re-fetch it.
124+
* If we are not sitting on a row, we still have to start up and
125+
* shut down the executor so that the destination is initialized
126+
* and shut down correctly; so keep going. Further down in the
127+
* routine, count == 0 means we will retrieve no row.
128+
*/
129+
if (on_row)
130+
{
131+
PerformPortalFetch(name, false /* backward */, 1L,
132+
None, /* throw away output */
133+
NULL /* do not modify the command tag */);
134+
/* Set up to fetch one row forward */
135+
count = 1;
136+
forward = true;
137+
}
138138
}
139139
}
140140

141-
/* Internally, zero count processes all portal rows */
142-
if (count == LONG_MAX)
143-
count = 0;
144-
145141
/*
146142
* switch into the portal context
147143
*/
@@ -185,31 +181,45 @@ PerformPortalFetch(char *name,
185181
*/
186182
if (forward)
187183
{
188-
if (portal->atEnd)
184+
if (portal->atEnd || count == 0)
189185
direction = NoMovementScanDirection;
190186
else
191187
direction = ForwardScanDirection;
192188

193-
ExecutorRun(queryDesc, direction, (long) count);
189+
/* In the executor, zero count processes all portal rows */
190+
if (count == INT_MAX)
191+
count = 0;
194192

195-
if (estate->es_processed > 0)
196-
portal->atStart = false; /* OK to back up now */
197-
if (count <= 0 || (int) estate->es_processed < count)
198-
portal->atEnd = true; /* we retrieved 'em all */
193+
ExecutorRun(queryDesc, direction, count);
194+
195+
if (direction != NoMovementScanDirection)
196+
{
197+
if (estate->es_processed > 0)
198+
portal->atStart = false; /* OK to back up now */
199+
if (count <= 0 || (long) estate->es_processed < count)
200+
portal->atEnd = true; /* we retrieved 'em all */
201+
}
199202
}
200203
else
201204
{
202-
if (portal->atStart)
205+
if (portal->atStart || count == 0)
203206
direction = NoMovementScanDirection;
204207
else
205208
direction = BackwardScanDirection;
206209

207-
ExecutorRun(queryDesc, direction, (long) count);
210+
/* In the executor, zero count processes all portal rows */
211+
if (count == INT_MAX)
212+
count = 0;
213+
214+
ExecutorRun(queryDesc, direction, count);
208215

209-
if (estate->es_processed > 0)
210-
portal->atEnd = false; /* OK to go forward now */
211-
if (count <= 0 || (int) estate->es_processed < count)
212-
portal->atStart = true; /* we retrieved 'em all */
216+
if (direction != NoMovementScanDirection)
217+
{
218+
if (estate->es_processed > 0)
219+
portal->atEnd = false; /* OK to go forward now */
220+
if (count <= 0 || (long) estate->es_processed < count)
221+
portal->atStart = true; /* we retrieved 'em all */
222+
}
213223
}
214224

215225
/* Return command status if wanted */

‎src/backend/parser/gram.y

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
*
1212
*
1313
* IDENTIFICATION
14-
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.390 2003/01/06 00:31:44 tgl Exp $
14+
* $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.391 2003/01/08 00:22:27 tgl Exp $
1515
*
1616
* HISTORY
1717
* AUTHOR DATE MAJOR EVENT
@@ -2594,7 +2594,7 @@ FetchStmt: FETCH direction fetch_how_many from_in name
25942594
if ($3 < 0)
25952595
{
25962596
$3 = -$3;
2597-
$2 = (($2 == FORWARD)? BACKWARD: FORWARD);
2597+
$2 = (($2 == FORWARD) ? BACKWARD : FORWARD);
25982598
}
25992599
n->direction = $2;
26002600
n->howMany = $3;
@@ -2652,7 +2652,7 @@ FetchStmt: FETCH direction fetch_how_many from_in name
26522652
if ($3 < 0)
26532653
{
26542654
$3 = -$3;
2655-
$2 = (($2 == FORWARD) ? BACKWARD: FORWARD);
2655+
$2 = (($2 == FORWARD) ? BACKWARD : FORWARD);
26562656
}
26572657
n->direction = $2;
26582658
n->howMany = $3;
@@ -2720,8 +2720,8 @@ direction: FORWARD { $$ = FORWARD; }
27202720
fetch_how_many:
27212721
Iconst { $$ = $1; }
27222722
| '-' Iconst { $$ = - $2; }
2723-
| ALL { $$ = LONG_MAX; }
2724-
| LAST { $$ = LONG_MAX; }
2723+
| ALL { $$ = INT_MAX; }
2724+
| LAST { $$ = INT_MAX; }
27252725
| NEXT { $$ = 1; }
27262726
| PRIOR { $$ = -1; }
27272727
;
@@ -7115,8 +7115,8 @@ unreserved_keyword:
71157115
| INVOKER
71167116
| ISOLATION
71177117
| KEY
7118-
| LANGUAGE
71197118
| LANCOMPILER
7119+
| LANGUAGE
71207120
| LAST
71217121
| LEVEL
71227122
| LISTEN

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