On 18.02.21 19:14, Peter Eisentraut wrote:
On 18.02.21 17:11, David G. Johnston wrote:
The OP was doing a course based on Oracle and was confused regarding
our behavior. The documentation failed to help me provide a useful
response, so I'd agree there is something here that needs reworking if
not outright fixing.
According to the piece of the standard that I posted, the sensitivity
behavior here is implementation-dependent (not even -defined), so both
implementations are correct.
But the poster was apparently also confused by the same piece of
documentation.
I came up with the attached patch to sort this out a bit. It does not
change any cursor behavior. But the documentation now uses the terms
more correctly and explains the differences between SQL and the
PostgreSQL implementation better, I think.
From 988206ec56a9def21b67f0cc871be3501e6af846 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Thu, 25 Feb 2021 16:25:57 +0100
Subject: [PATCH] Fix use of cursor sensitivity terminology
Documentation and comments in code and tests have been using the terms
sensitive/insensitive cursor incorrectly relative to the SQL standard.
(Cursor sensitivity is only relevant for changes made in the same
transaction as the cursor, not for concurrent changes in other
sessions.) Moreover, some of the behavior of PostgreSQL incorrect
according to the SQL standard, confusing the issue further. (WHERE
CURRENT OF changes are not visible in insensitive cursors, but they
should be.)
This change corrects the terminology and removes the claim that
sensitive cursors are supported. It also adds a test case that checks
the insensitive behavior in a "correct" way, using a change command
not using WHERE CURRENT OF. Finally, it adds the ASENSITIVE cursor
option to select the default asensitive behavior, per SQL standard.
There are no changes to cursor behavior in this patch.
Discussion:
https://www.postgresql.org/message-id/flat/96ee8b30-9889-9e1b-b053-90e10c050e85%40enterprisedb.com
---
doc/src/sgml/ecpg.sgml | 4 +--
doc/src/sgml/ref/declare.sgml | 49 ++++++++++++++++-----------
src/backend/catalog/sql_features.txt | 2 +-
src/backend/parser/analyze.c | 19 +++++++----
src/backend/parser/gram.y | 7 ++--
src/bin/psql/tab-complete.c | 2 +-
src/include/nodes/parsenodes.h | 1 +
src/include/parser/kwlist.h | 1 +
src/test/regress/expected/portals.out | 37 +++++++++++++++++++-
src/test/regress/sql/portals.sql | 17 +++++++++-
10 files changed, 105 insertions(+), 34 deletions(-)
diff --git a/doc/src/sgml/ecpg.sgml b/doc/src/sgml/ecpg.sgml
index 9310a71166..b36c9624f6 100644
--- a/doc/src/sgml/ecpg.sgml
+++ b/doc/src/sgml/ecpg.sgml
@@ -6752,8 +6752,8 @@ <title>See Also</title>
<refsynopsisdiv>
<synopsis>
-DECLARE <replaceable class="parameter">cursor_name</replaceable> [ BINARY ] [
INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR
<replaceable class="parameter">prepared_name</replaceable>
-DECLARE <replaceable class="parameter">cursor_name</replaceable> [ BINARY ] [
INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ] FOR
<replaceable class="parameter">query</replaceable>
+DECLARE <replaceable class="parameter">cursor_name</replaceable> [ BINARY ] [
ASENSITIVE | INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ]
FOR <replaceable class="parameter">prepared_name</replaceable>
+DECLARE <replaceable class="parameter">cursor_name</replaceable> [ BINARY ] [
ASENSITIVE | INSENSITIVE ] [ [ NO ] SCROLL ] CURSOR [ { WITH | WITHOUT } HOLD ]
FOR <replaceable class="parameter">query</replaceable>
</synopsis>
</refsynopsisdiv>
diff --git a/doc/src/sgml/ref/declare.sgml b/doc/src/sgml/ref/declare.sgml
index 2152134635..8a2b8cc892 100644
--- a/doc/src/sgml/ref/declare.sgml
+++ b/doc/src/sgml/ref/declare.sgml
@@ -26,7 +26,7 @@
<refsynopsisdiv>
<synopsis>
-DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [
INSENSITIVE ] [ [ NO ] SCROLL ]
+DECLARE <replaceable class="parameter">name</replaceable> [ BINARY ] [
ASENSITIVE | INSENSITIVE ] [ [ NO ] SCROLL ]
CURSOR [ { WITH | WITHOUT } HOLD ] FOR <replaceable
class="parameter">query</replaceable>
</synopsis>
</refsynopsisdiv>
@@ -75,14 +75,25 @@ <title>Parameters</title>
</varlistentry>
<varlistentry>
+ <term><literal>ASENSITIVE</literal></term>
<term><literal>INSENSITIVE</literal></term>
<listitem>
<para>
- Indicates that data retrieved from the cursor should be
- unaffected by updates to the table(s) underlying the cursor that occur
- after the cursor is created. In <productname>PostgreSQL</productname>,
- this is the default behavior; so this key word has no
- effect and is only accepted for compatibility with the SQL standard.
+ Cursor sensitivity determines whether changes to the data underlying the
+ cursor, done in the same transaction, after the cursor has been
+ declared, are visible in the cursor. <literal>INSENSITIVE</literal>
+ means they are not visible, <literal>ASENSITIVE</literal> means the
+ behavior is implementation-dependent. A third behavior,
+ <literal>SENSITIVE</literal>, meaning that such changes are visible in
+ the cursor, is not available in <productname>PostgreSQL</productname>.
+ In <productname>PostgreSQL</productname>, all cursors are insensitive;
+ so these key words have no effect and are only accepted for
+ compatibility with the SQL standard.
+ </para>
+
+ <para>
+ Specifying <literal>INSENSITIVE</literal> together with <literal>FOR
+ UPDATE</literal> or <literal>FOR SHARE</literal> is an error.
</para>
</listitem>
</varlistentry>
@@ -133,7 +144,7 @@ <title>Parameters</title>
</variablelist>
<para>
- The key words <literal>BINARY</literal>,
+ The key words <literal>ASENSITIVE</literal>, <literal>BINARY</literal>,
<literal>INSENSITIVE</literal>, and <literal>SCROLL</literal> can
appear in any order.
</para>
@@ -246,10 +257,7 @@ <title>Notes</title>
fetched, in the same way as for a regular
<link linkend="sql-select"><command>SELECT</command></link> command with
these options.
- In addition, the returned rows will be the most up-to-date versions;
- therefore these options provide the equivalent of what the SQL standard
- calls a <quote>sensitive cursor</quote>. (Specifying
<literal>INSENSITIVE</literal>
- together with <literal>FOR UPDATE</literal> or <literal>FOR
SHARE</literal> is an error.)
+ In addition, the returned rows will be the most up-to-date versions.
</para>
<caution>
@@ -278,7 +286,7 @@ <title>Notes</title>
<para>
The main reason not to use <literal>FOR UPDATE</literal> with
<literal>WHERE
CURRENT OF</literal> is if you need the cursor to be scrollable, or to be
- insensitive to the subsequent updates (that is, continue to show the old
+ isolated from concurrent updates (that is, continue to show the old
data). If this is a requirement, pay close heed to the caveats shown
above.
</para>
@@ -318,20 +326,21 @@ <title>Examples</title>
<refsect1>
<title>Compatibility</title>
- <para>
- The SQL standard says that it is implementation-dependent whether cursors
- are sensitive to concurrent updates of the underlying data by default. In
- <productname>PostgreSQL</productname>, cursors are insensitive by default,
- and can be made sensitive by specifying <literal>FOR UPDATE</literal>.
Other
- products may work differently.
- </para>
-
<para>
The SQL standard allows cursors only in embedded
<acronym>SQL</acronym> and in modules. <productname>PostgreSQL</productname>
permits cursors to be used interactively.
</para>
+ <para>
+ According to the SQL standard, changes made to insensitive cursors by
+ <literal>UPDATE ... WHERE CURRENT OF</literal> and <literal>DELETE
+ ... WHERE CURRENT OF</literal> statements are visibible in that same
+ cursor. <productname>PostgreSQL</productname> treats these statements like
+ all other data changing statements in that they are not visible in
+ insensitive cursors.
+ </para>
+
<para>
Binary cursors are a <productname>PostgreSQL</productname>
extension.
diff --git a/src/backend/catalog/sql_features.txt
b/src/backend/catalog/sql_features.txt
index a24387c1e7..e2a1bfbfed 100644
--- a/src/backend/catalog/sql_features.txt
+++ b/src/backend/catalog/sql_features.txt
@@ -451,7 +451,7 @@ T211 Basic trigger capability 07 TRIGGER
privilege YES
T211 Basic trigger capability 08 Multiple triggers for the same
event are executed in the order in which they were created in the catalog
NO intentionally omitted
T212 Enhanced trigger capability YES
T213 INSTEAD OF triggers YES
-T231 Sensitive cursors YES
+T231 Sensitive cursors NO
T241 START TRANSACTION statement YES
T251 SET TRANSACTION statement: LOCAL option NO
T261 Chained transactions YES
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 0f3a70c49a..0fb935bfb7 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -2679,14 +2679,21 @@ transformDeclareCursorStmt(ParseState *pstate,
DeclareCursorStmt *stmt)
Query *result;
Query *query;
- /*
- * Don't allow both SCROLL and NO SCROLL to be specified
- */
if ((stmt->options & CURSOR_OPT_SCROLL) &&
(stmt->options & CURSOR_OPT_NO_SCROLL))
ereport(ERROR,
(errcode(ERRCODE_INVALID_CURSOR_DEFINITION),
- errmsg("cannot specify both SCROLL and NO
SCROLL")));
+ /* translator: %s is a SQL keyword */
+ errmsg("cannot specify both %s and %s",
+ "SCROLL", "NO SCROLL")));
+
+ if ((stmt->options & CURSOR_OPT_ASENSITIVE) &&
+ (stmt->options & CURSOR_OPT_INSENSITIVE))
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_CURSOR_DEFINITION),
+ /* translator: %s is a SQL keyword */
+ errmsg("cannot specify both %s and %s",
+ "ASENSITIVE", "INSENSITIVE")));
/* Transform contained query, not allowing SELECT INTO */
query = transformStmt(pstate, stmt->query);
@@ -2732,10 +2739,10 @@ transformDeclareCursorStmt(ParseState *pstate,
DeclareCursorStmt *stmt)
/* FOR UPDATE and INSENSITIVE are not compatible */
if (query->rowMarks != NIL && (stmt->options & CURSOR_OPT_INSENSITIVE))
ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ (errcode(ERRCODE_INVALID_CURSOR_DEFINITION),
/*------
translator: %s is a SQL row locking clause such as FOR UPDATE
*/
- errmsg("DECLARE INSENSITIVE CURSOR ... %s is
not supported",
+ errmsg("DECLARE INSENSITIVE CURSOR ... %s is
not valid",
LCS_asString(((RowMarkClause *)
linitial(query->rowMarks))->strength)),
errdetail("Insensitive cursors must be READ
ONLY.")));
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index dd72a9fc3c..0a7839bbd4 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -623,7 +623,7 @@ static Node *makeRecursiveViewSelect(char *relname, List
*aliases, Node *query);
/* ordinary key words in alphabetical order */
%token <keyword> ABORT_P ABSOLUTE_P ACCESS ACTION ADD_P ADMIN AFTER
AGGREGATE ALL ALSO ALTER ALWAYS ANALYSE ANALYZE AND ANY ARRAY AS ASC
- ASSERTION ASSIGNMENT ASYMMETRIC AT ATTACH ATTRIBUTE AUTHORIZATION
+ ASENSITIVE ASSERTION ASSIGNMENT ASYMMETRIC AT ATTACH ATTRIBUTE
AUTHORIZATION
BACKWARD BEFORE BEGIN_P BETWEEN BIGINT BINARY BIT
BOOLEAN_P BOTH BREADTH BY
@@ -688,7 +688,7 @@ static Node *makeRecursiveViewSelect(char *relname, List
*aliases, Node *query);
RESET RESTART RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK
ROLLUP
ROUTINE ROUTINES ROW ROWS RULE
- SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
SEQUENCE SEQUENCES
+ SAVEPOINT SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
SEQUENCE SEQUENCES
SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SQL_P STABLE STANDALONE_P
START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRIP_P
@@ -11119,6 +11119,7 @@ cursor_options: /*EMPTY*/
{ $$ = 0; }
| cursor_options NO SCROLL { $$ = $1 |
CURSOR_OPT_NO_SCROLL; }
| cursor_options SCROLL { $$ = $1 |
CURSOR_OPT_SCROLL; }
| cursor_options BINARY { $$ = $1 |
CURSOR_OPT_BINARY; }
+ | cursor_options ASENSITIVE { $$ = $1 |
CURSOR_OPT_ASENSITIVE; }
| cursor_options INSENSITIVE { $$ = $1 |
CURSOR_OPT_INSENSITIVE; }
;
@@ -15258,6 +15259,7 @@ unreserved_keyword:
| ALSO
| ALTER
| ALWAYS
+ | ASENSITIVE
| ASSERTION
| ASSIGNMENT
| AT
@@ -15763,6 +15765,7 @@ bare_label_keyword:
| AND
| ANY
| ASC
+ | ASENSITIVE
| ASSERTION
| ASSIGNMENT
| ASYMMETRIC
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 9f0208ac49..9abdd36603 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -3050,7 +3050,7 @@ psql_completion(const char *text, int start, int end)
* SCROLL, and CURSOR.
*/
else if (Matches("DECLARE", MatchAny))
- COMPLETE_WITH("BINARY", "INSENSITIVE", "SCROLL", "NO SCROLL",
+ COMPLETE_WITH("BINARY", "ASENSITIVE", "INSENSITIVE", "SCROLL",
"NO SCROLL",
"CURSOR");
/*
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 236832a2ca..90e29fae8c 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -2751,6 +2751,7 @@ typedef struct SecLabelStmt
#define CURSOR_OPT_SCROLL 0x0002 /* SCROLL explicitly given */
#define CURSOR_OPT_NO_SCROLL 0x0004 /* NO SCROLL explicitly given */
#define CURSOR_OPT_INSENSITIVE 0x0008 /* INSENSITIVE */
+#define CURSOR_OPT_ASENSITIVE 0x0200 /* ASENSITIVE */
#define CURSOR_OPT_HOLD 0x0010 /* WITH HOLD */
/* these planner-control flags do not correspond to any SQL grammar: */
#define CURSOR_OPT_FAST_PLAN 0x0020 /* prefer fast-start plan */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 28083aaac9..31dc65dbc0 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -44,6 +44,7 @@ PG_KEYWORD("any", ANY, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("array", ARRAY, RESERVED_KEYWORD, AS_LABEL)
PG_KEYWORD("as", AS, RESERVED_KEYWORD, AS_LABEL)
PG_KEYWORD("asc", ASC, RESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("asensitive", ASENSITIVE, UNRESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("assertion", ASSERTION, UNRESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("assignment", ASSIGNMENT, UNRESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("asymmetric", ASYMMETRIC, RESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/test/regress/expected/portals.out
b/src/test/regress/expected/portals.out
index dc0d2ef7dd..42dc637fd4 100644
--- a/src/test/regress/expected/portals.out
+++ b/src/test/regress/expected/portals.out
@@ -1094,7 +1094,7 @@ SELECT * FROM uctest;
8 | one
(1 row)
---- sensitive cursors can't currently scroll back, so this is an error:
+--- FOR UPDATE cursors can't currently scroll back, so this is an error:
FETCH RELATIVE 0 FROM c1;
ERROR: cursor can only scan forward
HINT: Declare it with SCROLL option to enable backward scan.
@@ -1106,6 +1106,41 @@ SELECT * FROM uctest;
8 | one
(2 rows)
+-- Check insensitive cursor with INSERT
+-- (The above tests don't test the SQL notion of an insensitive cursor
+-- correctly, because per SQL standard, changes from WHERE CURRENT OF
+-- commands should be visible in the cursor. So here we make the
+-- changes with a command that is independent of the cursor.)
+BEGIN;
+DECLARE c1 INSENSITIVE CURSOR FOR SELECT * FROM uctest;
+INSERT INTO uctest VALUES (10, 'ten');
+FETCH NEXT FROM c1;
+ f1 | f2
+----+-------
+ 3 | three
+(1 row)
+
+FETCH NEXT FROM c1;
+ f1 | f2
+----+-----
+ 8 | one
+(1 row)
+
+FETCH NEXT FROM c1; -- insert not visible
+ f1 | f2
+----+----
+(0 rows)
+
+COMMIT;
+SELECT * FROM uctest;
+ f1 | f2
+----+-------
+ 3 | three
+ 8 | one
+ 10 | ten
+(3 rows)
+
+DELETE FROM uctest WHERE f1 = 10; -- restore test table state
-- Check inheritance cases
CREATE TEMP TABLE ucchild () inherits (uctest);
INSERT INTO ucchild values(100, 'hundred');
diff --git a/src/test/regress/sql/portals.sql b/src/test/regress/sql/portals.sql
index 52560ac027..bf1dff884d 100644
--- a/src/test/regress/sql/portals.sql
+++ b/src/test/regress/sql/portals.sql
@@ -382,11 +382,26 @@ CREATE TEMP TABLE uctest(f1 int, f2 text);
SELECT * FROM uctest;
UPDATE uctest SET f1 = f1 + 10 WHERE CURRENT OF c1; -- no-op
SELECT * FROM uctest;
---- sensitive cursors can't currently scroll back, so this is an error:
+--- FOR UPDATE cursors can't currently scroll back, so this is an error:
FETCH RELATIVE 0 FROM c1;
ROLLBACK;
SELECT * FROM uctest;
+-- Check insensitive cursor with INSERT
+-- (The above tests don't test the SQL notion of an insensitive cursor
+-- correctly, because per SQL standard, changes from WHERE CURRENT OF
+-- commands should be visible in the cursor. So here we make the
+-- changes with a command that is independent of the cursor.)
+BEGIN;
+DECLARE c1 INSENSITIVE CURSOR FOR SELECT * FROM uctest;
+INSERT INTO uctest VALUES (10, 'ten');
+FETCH NEXT FROM c1;
+FETCH NEXT FROM c1;
+FETCH NEXT FROM c1; -- insert not visible
+COMMIT;
+SELECT * FROM uctest;
+DELETE FROM uctest WHERE f1 = 10; -- restore test table state
+
-- Check inheritance cases
CREATE TEMP TABLE ucchild () inherits (uctest);
INSERT INTO ucchild values(100, 'hundred');
--
2.30.1
