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Commitd57c7a7

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Provide a test for variable existence in psql
"\if :{?variable_name}" will be translated to "\if TRUE" if the variableexists and "\if FALSE" otherwise. Thus it will be possible to execute codeconditionally on the existence of the variable, regardless of its value.Fabien Coelho, with some review by Robins Tharakan and some light textediting by me.Discussion:https://postgr.es/m/alpine.DEB.2.20.1708260835520.3627@lancre
1 parent7148050 commitd57c7a7

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6 files changed

+115
-1
lines changed

6 files changed

+115
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lines changed

‎doc/src/sgml/ref/psql-ref.sgml

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Original file line numberDiff line numberDiff line change
@@ -783,6 +783,10 @@ testdb=>
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The forms <literal>:'<replaceable>variable_name</>'</literal> and
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<literal>:"<replaceable>variable_name</>"</literal> described there
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work as well.
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The <literal>:{?<replaceable>variable_name</>}</> syntax allows
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testing whether a variable is defined. It is substituted by
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TRUE or FALSE.
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Escaping the colon with a backslash protects it from substitution.
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</para>
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<para>
@@ -3938,6 +3942,12 @@ testdb=&gt; <userinput>INSERT INTO my_table VALUES (:'content');</userinput>
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can escape a colon with a backslash to protect it from substitution.
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</para>
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<para>
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The <literal>:{?<replaceable>name</>}</> special syntax returns TRUE
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or FALSE depending on whether the variable exists or not, and is thus
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always substituted, unless the colon is backslash-escaped.
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</para>
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<para>
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The colon syntax for variables is standard <acronym>SQL</acronym> for
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embedded query languages, such as <application>ECPG</application>.

‎src/bin/psql/psqlscanslash.l

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@@ -281,6 +281,10 @@ other.
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unquoted_option_chars =0;
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}
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:\{\?{variable_char}+\}{
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psqlscan_test_variable(cur_state, yytext, yyleng);
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}
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:'{variable_char}*{
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/* Throw back everything but the colon */
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yyless(1);
@@ -295,6 +299,20 @@ other.
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ECHO;
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}
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:\{\?{variable_char}*{
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/* Throw back everything but the colon */
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yyless(1);
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unquoted_option_chars++;
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ECHO;
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}
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:\{{
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/* Throw back everything but the colon */
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yyless(1);
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unquoted_option_chars++;
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ECHO;
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}
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{other}{
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unquoted_option_chars++;
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ECHO;

‎src/fe_utils/psqlscan.l

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Original file line numberDiff line numberDiff line change
@@ -745,9 +745,13 @@ other.
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PQUOTE_SQL_IDENT);
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}
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:\{\?{variable_char}+\}{
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psqlscan_test_variable(cur_state, yytext, yyleng);
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}
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/*
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* These rules just avoid the need for scanner backup if one of the
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*two rules above fails to match completely.
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*three rules above fails to match completely.
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*/
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:'{variable_char}*{
@@ -762,6 +766,17 @@ other.
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ECHO;
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}
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:\{\?{variable_char}*{
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/* Throw back everything but the colon */
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yyless(1);
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ECHO;
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}
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:\{{
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/* Throw back everything but the colon */
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yyless(1);
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ECHO;
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}
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/*
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* Back to backend-compatible rules.
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*/
@@ -1442,3 +1457,28 @@ psqlscan_escape_variable(PsqlScanState state, const char *txt, int len,
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psqlscan_emit(state, txt, len);
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}
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}
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void
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psqlscan_test_variable(PsqlScanState state,constchar *txt,int len)
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{
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char*varname;
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char*value;
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varname =psqlscan_extract_substring(state, txt +3, len -4);
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if (state->callbacks->get_variable)
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value = state->callbacks->get_variable(varname, PQUOTE_PLAIN,
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state->cb_passthrough);
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else
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value =NULL;
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free(varname);
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if (value !=NULL)
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{
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psqlscan_emit(state,"TRUE",4);
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free(value);
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}
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else
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{
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psqlscan_emit(state,"FALSE",5);
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}
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}

‎src/include/fe_utils/psqlscan_int.h

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Original file line numberDiff line numberDiff line change
@@ -142,5 +142,7 @@ extern char *psqlscan_extract_substring(PsqlScanState state,
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externvoidpsqlscan_escape_variable(PsqlScanStatestate,
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constchar*txt,intlen,
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PsqlScanQuoteTypequote);
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externvoidpsqlscan_test_variable(PsqlScanStatestate,
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constchar*txt,intlen);
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#endif/* PSQLSCAN_INT_H */

‎src/test/regress/expected/psql.out

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@@ -3014,6 +3014,32 @@ bar 'bar' "bar"
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\echo 'should print #8-1'
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should print #8-1
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\endif
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-- :{?...} defined variable test
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\set i 1
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\if :{?i}
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\echo '#9-1 ok, variable i is defined'
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#9-1 ok, variable i is defined
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\else
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\echo 'should not print #9-2'
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\endif
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\if :{?no_such_variable}
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\echo 'should not print #10-1'
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\else
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\echo '#10-2 ok, variable no_such_variable is not defined'
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#10-2 ok, variable no_such_variable is not defined
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\endif
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SELECT :{?i} AS i_is_defined;
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i_is_defined
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--------------
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t
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(1 row)
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SELECT NOT :{?no_such_var} AS no_such_var_is_not_defined;
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no_such_var_is_not_defined
3039+
----------------------------
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t
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(1 row)
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-- SHOW_CONTEXT
30183044
\set SHOW_CONTEXT never
30193045
do $$

‎src/test/regress/sql/psql.sql

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Original file line numberDiff line numberDiff line change
@@ -572,6 +572,24 @@ select \if false \\ (bogus \else \\ 42 \endif \\ forty_two;
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\echo'should print #8-1'
573573
\endif
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-- :{?...} defined variable test
576+
\set i1
577+
\if :{?i}
578+
\echo'#9-1 ok, variable i is defined'
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\else
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\echo'should not print #9-2'
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\endif
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\if :{?no_such_variable}
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\echo'should not print #10-1'
585+
\else
586+
\echo'#10-2 ok, variable no_such_variable is not defined'
587+
\endif
588+
589+
SELECT :{?i}AS i_is_defined;
590+
591+
SELECT NOT :{?no_such_var}AS no_such_var_is_not_defined;
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575593
-- SHOW_CONTEXT
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577595
\set SHOW_CONTEXT never

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