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Support EXECUTE USING in plpgsql.
Pavel Stehule, with some improvements by myself.
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‎doc/src/sgml/plpgsql.sgml

Lines changed: 57 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.125 2008/03/28 00:21:55 tgl Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.126 2008/04/01 03:51:09 tgl Exp $ -->
22

33
<chapter id="plpgsql">
44
<title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -1005,20 +1005,23 @@ END;
10051005
<command>EXECUTE</command> statement is provided:
10061006

10071007
<synopsis>
1008-
EXECUTE <replaceable class="command">command-string</replaceable> <optional> INTO <optional>STRICT</optional> <replaceable>target</replaceable> </optional>;
1008+
EXECUTE <replaceable class="command">command-string</replaceable> <optional> INTO <optional>STRICT</optional> <replaceable>target</replaceable> </optional> <optional> USING <replaceable>expression</replaceable> <optional>, ...</optional> </optional>;
10091009
</synopsis>
10101010

10111011
where <replaceable>command-string</replaceable> is an expression
10121012
yielding a string (of type <type>text</type>) containing the
1013-
command to be executed and <replaceable>target</replaceable> is a
1014-
record variable, row variable, or a comma-separated list of
1015-
simple variables and record/row fields.
1013+
command to be executed. The optional <replaceable>target</replaceable>
1014+
is a record variable, a row variable, or a comma-separated list of
1015+
simple variables and record/row fields, into which the results of
1016+
the command will be stored. The optional <literal>USING</> expressions
1017+
supply values to be inserted into the command.
10161018
</para>
10171019

10181020
<para>
10191021
No substitution of <application>PL/pgSQL</> variables is done on the
10201022
computed command string. Any required variable values must be inserted
1021-
in the command string as it is constructed.
1023+
in the command string as it is constructed; or you can use parameters
1024+
as described below.
10221025
</para>
10231026

10241027
<para>
@@ -1046,6 +1049,51 @@ EXECUTE <replaceable class="command">command-string</replaceable> <optional> INT
10461049
If the <literal>STRICT</> option is given, an error is reported
10471050
unless the query produces exactly one row.
10481051
</para>
1052+
1053+
<para>
1054+
The command string can use parameter values, which are referenced
1055+
in the command as <literal>$1</>, <literal>$2</>, etc.
1056+
These symbols refer to values supplied in the <literal>USING</>
1057+
clause. This method is often preferable to inserting data values
1058+
into the command string as text: it avoids run-time overhead of
1059+
converting the values to text and back, and it is much less prone
1060+
to SQL-injection attacks since there is no need for quoting or escaping.
1061+
An example is:
1062+
<programlisting>
1063+
EXECUTE 'SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2'
1064+
INTO c
1065+
USING checked_user, checked_date;
1066+
</programlisting>
1067+
1068+
Note that parameter symbols can only be used for data values
1069+
&mdash; if you want to use dynamically determined table or column
1070+
names, you must insert them into the command string textually.
1071+
For example, if the preceding query needed to be done against a
1072+
dynamically selected table, you could do this:
1073+
<programlisting>
1074+
EXECUTE 'SELECT count(*) FROM '
1075+
|| tabname::regclass
1076+
|| ' WHERE inserted_by = $1 AND inserted <= $2'
1077+
INTO c
1078+
USING checked_user, checked_date;
1079+
</programlisting>
1080+
</para>
1081+
1082+
<para>
1083+
An <command>EXECUTE</> with a simple constant command string and some
1084+
<literal>USING</> parameters, as in the first example above, is
1085+
functionally equivalent to just writing the command directly in
1086+
<application>PL/pgSQL</application> and allowing replacement of
1087+
<application>PL/pgSQL</application> variables to happen automatically.
1088+
The important difference is that <command>EXECUTE</> will re-plan
1089+
the command on each execution, generating a plan that is specific
1090+
to the current parameter values; whereas
1091+
<application>PL/pgSQL</application> normally creates a generic plan
1092+
and caches it for re-use. In situations where the best plan depends
1093+
strongly on the parameter values, <command>EXECUTE</> can be
1094+
significantly faster; while when the plan is not sensitive to parameter
1095+
values, re-planning will be a waste.
1096+
</para>
10491097

10501098
<para>
10511099
<command>SELECT INTO</command> is not currently supported within
@@ -1997,7 +2045,7 @@ $$ LANGUAGE plpgsql;
19972045
rows:
19982046
<synopsis>
19992047
<optional> &lt;&lt;<replaceable>label</replaceable>&gt;&gt; </optional>
2000-
FOR <replaceable>target</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> LOOP
2048+
FOR <replaceable>target</replaceable> IN EXECUTE <replaceable>text_expression</replaceable> <optional> USING <replaceable>expression</replaceable> <optional>, ...</optional> </optional> LOOP
20012049
<replaceable>statements</replaceable>
20022050
END LOOP <optional> <replaceable>label</replaceable> </optional>;
20032051
</synopsis>
@@ -2006,6 +2054,8 @@ END LOOP <optional> <replaceable>label</replaceable> </optional>;
20062054
on each entry to the <literal>FOR</> loop. This allows the programmer to
20072055
choose the speed of a preplanned query or the flexibility of a dynamic
20082056
query, just as with a plain <command>EXECUTE</command> statement.
2057+
As with <command>EXECUTE</command>, parameter values can be inserted
2058+
into the dynamic command via <literal>USING</>.
20092059
</para>
20102060
</sect2>
20112061

‎src/pl/plpgsql/src/gram.y

Lines changed: 82 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@
99
*
1010
*
1111
* IDENTIFICATION
12-
* $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.108 2008/01/01 19:46:00 momjian Exp $
12+
* $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.109 2008/04/01 03:51:09 tgl Exp $
1313
*
1414
*-------------------------------------------------------------------------
1515
*/
@@ -21,11 +21,15 @@
2121

2222
static PLpgSQL_expr *read_sql_construct(int until,
2323
int until2,
24+
int until3,
2425
const char *expected,
2526
const char *sqlstart,
2627
bool isexpression,
2728
bool valid_sql,
2829
int *endtoken);
30+
static PLpgSQL_expr *read_sql_expression2(int until, int until2,
31+
const char *expected,
32+
int *endtoken);
2933
static PLpgSQL_expr *read_sql_stmt(const char *sqlstart);
3034
static PLpgSQL_type *read_datatype(int tok);
3135
static PLpgSQL_stmt *make_execsql_stmt(const char *sqlstart, int lineno);
@@ -200,6 +204,7 @@ static void check_labels(const char *start_label,
200204
%token K_THEN
201205
%token K_TO
202206
%token K_TYPE
207+
%token K_USING
203208
%token K_WARNING
204209
%token K_WHEN
205210
%token K_WHILE
@@ -892,8 +897,11 @@ for_control :
892897
{
893898
PLpgSQL_stmt_dynfors *new;
894899
PLpgSQL_expr *expr;
900+
int term;
895901

896-
expr = plpgsql_read_expression(K_LOOP, "LOOP");
902+
expr = read_sql_expression2(K_LOOP, K_USING,
903+
"LOOP or USING",
904+
&term);
897905

898906
new = palloc0(sizeof(PLpgSQL_stmt_dynfors));
899907
new->cmd_type = PLPGSQL_STMT_DYNFORS;
@@ -921,6 +929,17 @@ for_control :
921929
}
922930
new->query = expr;
923931

932+
if (term == K_USING)
933+
{
934+
do
935+
{
936+
expr = read_sql_expression2(',', K_LOOP,
937+
", or LOOP",
938+
&term);
939+
new->params = lappend(new->params, expr);
940+
} while (term == ',');
941+
}
942+
924943
$$ = (PLpgSQL_stmt *) new;
925944
}
926945
else
@@ -954,6 +973,7 @@ for_control :
954973
*/
955974
expr1 = read_sql_construct(K_DOTDOT,
956975
K_LOOP,
976+
0,
957977
"LOOP",
958978
"SELECT ",
959979
true,
@@ -973,17 +993,14 @@ for_control :
973993
check_sql_expr(expr1->query);
974994

975995
/* Read and check the second one */
976-
expr2 = read_sql_construct(K_LOOP,
977-
K_BY,
978-
"LOOP",
979-
"SELECT ",
980-
true,
981-
true,
982-
&tok);
996+
expr2 = read_sql_expression2(K_LOOP, K_BY,
997+
"LOOP",
998+
&tok);
983999

9841000
/* Get the BY clause if any */
9851001
if (tok == K_BY)
986-
expr_by = plpgsql_read_expression(K_LOOP, "LOOP");
1002+
expr_by = plpgsql_read_expression(K_LOOP,
1003+
"LOOP");
9871004
else
9881005
expr_by = NULL;
9891006

@@ -1217,18 +1234,15 @@ stmt_raise : K_RAISE lno raise_level raise_msg
12171234

12181235
if (tok == ',')
12191236
{
1220-
PLpgSQL_expr *expr;
1221-
int term;
1222-
1223-
for (;;)
1237+
do
12241238
{
1225-
expr = read_sql_construct(',', ';', ", or ;",
1226-
"SELECT ",
1227-
true, true, &term);
1239+
PLpgSQL_expr *expr;
1240+
1241+
expr = read_sql_expression2(',', ';',
1242+
", or ;",
1243+
&tok);
12281244
new->params = lappend(new->params, expr);
1229-
if (term == ';')
1230-
break;
1231-
}
1245+
} while (tok == ',');
12321246
}
12331247

12341248
$$ = (PLpgSQL_stmt *)new;
@@ -1307,7 +1321,8 @@ stmt_dynexecute : K_EXECUTE lno
13071321
PLpgSQL_expr *expr;
13081322
int endtoken;
13091323

1310-
expr = read_sql_construct(K_INTO, ';', "INTO|;",
1324+
expr = read_sql_construct(K_INTO, K_USING, ';',
1325+
"INTO or USING or ;",
13111326
"SELECT ",
13121327
true, true, &endtoken);
13131328

@@ -1319,16 +1334,30 @@ stmt_dynexecute : K_EXECUTE lno
13191334
new->strict = false;
13201335
new->rec = NULL;
13211336
new->row = NULL;
1337+
new->params = NIL;
13221338

13231339
/* If we found "INTO", collect the argument */
13241340
if (endtoken == K_INTO)
13251341
{
13261342
new->into = true;
13271343
read_into_target(&new->rec, &new->row, &new->strict);
1328-
if (yylex() != ';')
1344+
endtoken = yylex();
1345+
if (endtoken != ';' && endtoken != K_USING)
13291346
yyerror("syntax error");
13301347
}
13311348

1349+
/* If we found "USING", collect the argument(s) */
1350+
if (endtoken == K_USING)
1351+
{
1352+
do
1353+
{
1354+
expr = read_sql_expression2(',', ';',
1355+
", or ;",
1356+
&endtoken);
1357+
new->params = lappend(new->params, expr);
1358+
} while (endtoken == ',');
1359+
}
1360+
13321361
$$ = (PLpgSQL_stmt *)new;
13331362
}
13341363
;
@@ -1485,7 +1514,7 @@ stmt_fetch : K_FETCH lno opt_fetch_direction cursor_variable K_INTO
14851514
$$ = (PLpgSQL_stmt *)fetch;
14861515
}
14871516
;
1488-
1517+
14891518
stmt_move : K_MOVE lno opt_fetch_direction cursor_variable ';'
14901519
{
14911520
PLpgSQL_stmt_fetch *fetch = $3;
@@ -1730,33 +1759,48 @@ assign_expr_param(int dno, int *params, int *nparams)
17301759
}
17311760

17321761

1762+
/* Convenience routine to read an expression with one possible terminator */
17331763
PLpgSQL_expr *
17341764
plpgsql_read_expression(int until, const char *expected)
17351765
{
1736-
return read_sql_construct(until, 0, expected, "SELECT ", true, true, NULL);
1766+
return read_sql_construct(until, 0, 0, expected,
1767+
"SELECT ", true, true, NULL);
17371768
}
17381769

1770+
/* Convenience routine to read an expression with two possible terminators */
1771+
static PLpgSQL_expr *
1772+
read_sql_expression2(int until, int until2, const char *expected,
1773+
int *endtoken)
1774+
{
1775+
return read_sql_construct(until, until2, 0, expected,
1776+
"SELECT ", true, true, endtoken);
1777+
}
1778+
1779+
/* Convenience routine to read a SQL statement that must end with ';' */
17391780
static PLpgSQL_expr *
17401781
read_sql_stmt(const char *sqlstart)
17411782
{
1742-
return read_sql_construct(';', 0, ";", sqlstart, false, true, NULL);
1783+
return read_sql_construct(';', 0, 0, ";",
1784+
sqlstart, false, true, NULL);
17431785
}
17441786

17451787
/*
17461788
* Read a SQL construct and build a PLpgSQL_expr for it.
17471789
*
17481790
* until: token code for expected terminator
17491791
* until2: token code for alternate terminator (pass 0 if none)
1792+
* until3: token code for another alternate terminator (pass 0 if none)
17501793
* expected: text to use in complaining that terminator was not found
17511794
* sqlstart: text to prefix to the accumulated SQL text
17521795
* isexpression: whether to say we're reading an "expression" or a "statement"
17531796
* valid_sql: whether to check the syntax of the expr (prefixed with sqlstart)
17541797
* endtoken: if not NULL, ending token is stored at *endtoken
1755-
* (this is only interesting if until2 isn't zero)
1798+
* (this is only interesting if until2 or until3 isn't zero)
17561799
*/
17571800
static PLpgSQL_expr *
17581801
read_sql_construct(int until,
17591802
int until2,
1803+
int until3,
17601804
const char *expected,
17611805
const char *sqlstart,
17621806
bool isexpression,
@@ -1783,6 +1827,8 @@ read_sql_construct(int until,
17831827
break;
17841828
if (tok == until2 && parenlevel == 0)
17851829
break;
1830+
if (tok == until3 && parenlevel == 0)
1831+
break;
17861832
if (tok == '(' || tok == '[')
17871833
parenlevel++;
17881834
else if (tok == ')' || tok == ']')
@@ -2066,15 +2112,17 @@ read_fetch_direction(void)
20662112
else if (pg_strcasecmp(yytext, "absolute") == 0)
20672113
{
20682114
fetch->direction = FETCH_ABSOLUTE;
2069-
fetch->expr = read_sql_construct(K_FROM, K_IN, "FROM or IN",
2070-
"SELECT ", true, true, NULL);
2115+
fetch->expr = read_sql_expression2(K_FROM, K_IN,
2116+
"FROM or IN",
2117+
NULL);
20712118
check_FROM = false;
20722119
}
20732120
else if (pg_strcasecmp(yytext, "relative") == 0)
20742121
{
20752122
fetch->direction = FETCH_RELATIVE;
2076-
fetch->expr = read_sql_construct(K_FROM, K_IN, "FROM or IN",
2077-
"SELECT ", true, true, NULL);
2123+
fetch->expr = read_sql_expression2(K_FROM, K_IN,
2124+
"FROM or IN",
2125+
NULL);
20782126
check_FROM = false;
20792127
}
20802128
else if (pg_strcasecmp(yytext, "forward") == 0)
@@ -2088,8 +2136,9 @@ read_fetch_direction(void)
20882136
else if (tok != T_SCALAR)
20892137
{
20902138
plpgsql_push_back_token(tok);
2091-
fetch->expr = read_sql_construct(K_FROM, K_IN, "FROM or IN",
2092-
"SELECT ", true, true, NULL);
2139+
fetch->expr = read_sql_expression2(K_FROM, K_IN,
2140+
"FROM or IN",
2141+
NULL);
20932142
check_FROM = false;
20942143
}
20952144
else
@@ -2233,7 +2282,7 @@ make_return_query_stmt(int lineno)
22332282
new = palloc0(sizeof(PLpgSQL_stmt_return_query));
22342283
new->cmd_type = PLPGSQL_STMT_RETURN_QUERY;
22352284
new->lineno = lineno;
2236-
new->query = read_sql_construct(';', 0, ")", "", false, true, NULL);
2285+
new->query = read_sql_stmt("");
22372286

22382287
return (PLpgSQL_stmt *) new;
22392288
}

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