Add \pset options for boolean value display

New \pset variables display_true and display_false allow the user to
change how true and false values are displayed.

Author: David G. Johnston <David.G.Johnston@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/CAKFQuwYts3vnfQ5AoKhEaKMTNMfJ443MW2kFswKwzn7fiofkrw@mail.gmail.com
Discussion: https://postgr.es/m/56308F56.8060908@joh.to

doc/src/sgml/ref/psql-ref.sgml

@@ -3099,6 +3099,26 @@ SELECT $1 \parse stmt1
           </listitem>
           </varlistentry>
 
+          <varlistentry id="app-psql-meta-command-pset-display-false">
+          <term><literal>display_false</literal></term>
+          <listitem>
+          <para>
+          Sets the string to be printed in place of a false value.
+          The default is to print <literal>f</literal>.
+          </para>
+          </listitem>
+          </varlistentry>
+
+          <varlistentry id="app-psql-meta-command-pset-display-true">
+          <term><literal>display_true</literal></term>
+          <listitem>
+          <para>
+          Sets the string to be printed in place of a true value.
+          The default is to print <literal>t</literal>.
+          </para>
+          </listitem>
+          </varlistentry>
+
           <varlistentry id="app-psql-meta-command-pset-expanded">
           <term><literal>expanded</literal> (or <literal>x</literal>)</term>
           <listitem>

src/bin/psql/command.c

@@ -2709,7 +2709,8 @@ exec_command_pset(PsqlScanState scan_state, bool active_branch)
 
 			int			i;
 			static const char *const my_list[] = {
-				"border", "columns", "csv_fieldsep", "expanded", "fieldsep",
+				"border", "columns", "csv_fieldsep",
+				"display_false", "display_true", "expanded", "fieldsep",
 				"fieldsep_zero", "footer", "format", "linestyle", "null",
 				"numericlocale", "pager", "pager_min_lines",
 				"recordsep", "recordsep_zero",
@@ -5300,6 +5301,26 @@ do_pset(const char *param, const char *value, printQueryOpt *popt, bool quiet)
 		}
 	}
 
+	/* 'false' display */
+	else if (strcmp(param, "display_false") == 0)
+	{
+		if (value)
+		{
+			free(popt->falsePrint);
+			popt->falsePrint = pg_strdup(value);
+		}
+	}
+
+	/* 'true' display */
+	else if (strcmp(param, "display_true") == 0)
+	{
+		if (value)
+		{
+			free(popt->truePrint);
+			popt->truePrint = pg_strdup(value);
+		}
+	}
+
 	/* field separator for unaligned text */
 	else if (strcmp(param, "fieldsep") == 0)
 	{
@@ -5474,6 +5495,20 @@ printPsetInfo(const char *param, printQueryOpt *popt)
 			   popt->topt.csvFieldSep);
 	}
 
+	/* show boolean 'false' display */
+	else if (strcmp(param, "display_false") == 0)
+	{
+		printf(_("Boolean false display is \"%s\".\n"),
+			   popt->falsePrint ? popt->falsePrint : "f");
+	}
+
+	/* show boolean 'true' display */
+	else if (strcmp(param, "display_true") == 0)
+	{
+		printf(_("Boolean true display is \"%s\".\n"),
+			   popt->truePrint ? popt->truePrint : "t");
+	}
+
 	/* show field separator for unaligned text */
 	else if (strcmp(param, "fieldsep") == 0)
 	{
@@ -5743,6 +5778,10 @@ pset_value_string(const char *param, printQueryOpt *popt)
 		return psprintf("%d", popt->topt.columns);
 	else if (strcmp(param, "csv_fieldsep") == 0)
 		return pset_quoted_string(popt->topt.csvFieldSep);
+	else if (strcmp(param, "display_false") == 0)
+		return pset_quoted_string(popt->falsePrint ? popt->falsePrint : "f");
+	else if (strcmp(param, "display_true") == 0)
+		return pset_quoted_string(popt->truePrint ? popt->truePrint : "t");
 	else if (strcmp(param, "expanded") == 0)
 		return pstrdup(popt->topt.expanded == 2
 					   ? "auto"

src/bin/psql/help.c

@@ -290,9 +290,9 @@ slashUsage(unsigned short int pager)
 	HELPN("  \\H                     toggle HTML output mode (currently %s)\n",
 		  ON(pset.popt.topt.format == PRINT_HTML));
 	HELP0("  \\pset [NAME [VALUE]]   set table output option\n"
-		  "                         (border|columns|csv_fieldsep|expanded|fieldsep|\n"
-		  "                         fieldsep_zero|footer|format|linestyle|null|\n"
-		  "                         numericlocale|pager|pager_min_lines|recordsep|\n"
+		  "                         (border|columns|csv_fieldsep|display_false|display_true|\n"
+		  "                         expanded|fieldsep|fieldsep_zero|footer|format|linestyle|\n"
+		  "                         null|numericlocale|pager|pager_min_lines|recordsep|\n"
 		  "                         recordsep_zero|tableattr|title|tuples_only|\n"
 		  "                         unicode_border_linestyle|unicode_column_linestyle|\n"
 		  "                         unicode_header_linestyle|xheader_width)\n");
@@ -480,6 +480,10 @@ helpVariables(unsigned short int pager)
 		  "    border style (number)\n");
 	HELP0("  columns\n"
 		  "    target width for the wrapped format\n");
+	HELP0("  display_false\n"
+		  "    set the string to be printed in place of a boolean 'false'\n");
+	HELP0("  display_true\n"
+		  "    set the string to be printed in place of a boolean 'true'\n");
 	HELP0("  expanded (or x)\n"
 		  "    expanded output [on, off, auto]\n");
 	HELPN("  fieldsep\n"

src/bin/psql/tab-complete.in.c

@@ -5478,7 +5478,8 @@ match_previous_words(int pattern_id,
 	else if (TailMatchesCS("\\password"))
 		COMPLETE_WITH_QUERY(Query_for_list_of_roles);
 	else if (TailMatchesCS("\\pset"))
-		COMPLETE_WITH_CS("border", "columns", "csv_fieldsep", "expanded",
+		COMPLETE_WITH_CS("border", "columns", "csv_fieldsep",
+						 "display_false", "display_true", "expanded",
 						 "fieldsep", "fieldsep_zero", "footer", "format",
 						 "linestyle", "null", "numericlocale",
 						 "pager", "pager_min_lines",

src/fe_utils/print.c

@@ -3775,6 +3775,10 @@ printQuery(const PGresult *result, const printQueryOpt *opt,
 
 			if (PQgetisnull(result, r, c))
 				cell = opt->nullPrint ? opt->nullPrint : "";
+			else if (PQftype(result, c) == BOOLOID)
+				cell = (PQgetvalue(result, r, c)[0] == 't' ?
+						(opt->truePrint ? opt->truePrint : "t") :
+						(opt->falsePrint ? opt->falsePrint : "f"));
 			else
 			{
 				cell = PQgetvalue(result, r, c);

src/include/fe_utils/print.h

@@ -184,6 +184,8 @@ typedef struct printQueryOpt
 {
 	printTableOpt topt;			/* the options above */
 	char	   *nullPrint;		/* how to print null entities */
+	char	   *truePrint;		/* how to print boolean true values */
+	char	   *falsePrint;		/* how to print boolean false values */
 	char	   *title;			/* override title */
 	char	  **footers;		/* override footer (default is "(xx rows)") */
 	bool		translate_header;	/* do gettext on column headers */

src/test/regress/expected/psql.out

@@ -445,6 +445,8 @@ environment value
 border                   1
 columns                  0
 csv_fieldsep             ','
+display_false            'f'
+display_true             't'
 expanded                 off
 fieldsep                 '|'
 fieldsep_zero            off
@@ -464,6 +466,36 @@ unicode_border_linestyle single
 unicode_column_linestyle single
 unicode_header_linestyle single
 xheader_width            full
+-- test the simple display substitution settings
+prepare q as select null as n, true as t, false as f;
+\pset null '(null)'
+\pset display_true 'true'
+\pset display_false 'false'
+execute q;
+   n    |  t   |   f   
+--------+------+-------
+ (null) | true | false
+(1 row)
+
+\pset null
+\pset display_true
+\pset display_false
+execute q;
+   n    |  t   |   f   
+--------+------+-------
+ (null) | true | false
+(1 row)
+
+\pset null ''
+\pset display_true 't'
+\pset display_false 'f'
+execute q;
+ n | t | f 
+---+---+---
+   | t | f
+(1 row)
+
+deallocate q;
 -- test multi-line headers, wrapping, and newline indicators
 -- in aligned, unaligned, and wrapped formats
 prepare q as select array_to_string(array_agg(repeat('x',2*n)),E'\n') as "ab

src/test/regress/sql/psql.sql

@@ -219,6 +219,22 @@ select 'drop table gexec_test', 'select ''2000-01-01''::date as party_over'
 -- show all pset options
 \pset
 
+-- test the simple display substitution settings
+prepare q as select null as n, true as t, false as f;
+\pset null '(null)'
+\pset display_true 'true'
+\pset display_false 'false'
+execute q;
+\pset null
+\pset display_true
+\pset display_false
+execute q;
+\pset null ''
+\pset display_true 't'
+\pset display_false 'f'
+execute q;
+deallocate q;
+
 -- test multi-line headers, wrapping, and newline indicators
 -- in aligned, unaligned, and wrapped formats
 prepare q as select array_to_string(array_agg(repeat('x',2*n)),E'\n') as "ab