psql: Show all query results by default

Previously, psql printed only the last result if a command string
returned multiple result sets.  Now it prints all of them.  The
previous behavior can be obtained by setting the psql variable
SHOW_ALL_RESULTS to off.

This is a significantly enhanced version of
3a51306 (that was later reverted).
There is also much more test coverage for various psql features now.

Author: Fabien COELHO <coelho@cri.ensmp.fr>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: "Iwata, Aya" <iwata.aya@jp.fujitsu.com> (earlier version)
Reviewed-by: Daniel Verite <daniel@manitou-mail.org> (earlier version)
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> (earlier version)
Reviewed-by: vignesh C <vignesh21@gmail.com> (earlier version)
Discussion: https://www.postgresql.org/message-id/flat/alpine.DEB.2.21.1904132231510.8961@lancre

Author: petere

contrib/pg_stat_statements/expected/pg_stat_statements.out

@@ -50,8 +50,28 @@ BEGIN \;
 SELECT 2.0 AS "float" \;
 SELECT 'world' AS "text" \;
 COMMIT;
+ float 
+-------
+   2.0
+(1 row)
+
+ text  
+-------
+ world
+(1 row)
+
 -- compound with empty statements and spurious leading spacing
 \;\;   SELECT 3 + 3 \;\;\;   SELECT ' ' || ' !' \;\;   SELECT 1 + 4 \;;
+ ?column? 
+----------
+        6
+(1 row)
+
+ ?column? 
+----------
+   !
+(1 row)
+
  ?column? 
 ----------
         5
@@ -61,6 +81,11 @@ COMMIT;
 SELECT 1 + 1 + 1 AS "add" \gset
 SELECT :add + 1 + 1 AS "add" \;
 SELECT :add + 1 + 1 AS "add" \gset
+ add 
+-----
+   5
+(1 row)
+
 -- set operator
 SELECT 1 AS i UNION SELECT 2 ORDER BY i;
  i 

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

@@ -127,18 +127,11 @@ echo '\x \\ SELECT * FROM foo;' | psql
        commands included in the string to divide it into multiple
        transactions.  (See <xref linkend="protocol-flow-multi-statement"/>
        for more details about how the server handles multi-query strings.)
-       Also, <application>psql</application> only prints the
-       result of the last <acronym>SQL</acronym> command in the string.
-       This is different from the behavior when the same string is read from
-       a file or fed to <application>psql</application>'s standard input,
-       because then <application>psql</application> sends
-       each <acronym>SQL</acronym> command separately.
       </para>
       <para>
-       Because of this behavior, putting more than one SQL command in a
-       single <option>-c</option> string often has unexpected results.
-       It's better to use repeated <option>-c</option> commands or feed
-       multiple commands to <application>psql</application>'s standard input,
+       If having several commands executed in one transaction is not desired, 
+       use repeated <option>-c</option> commands or feed multiple commands to
+       <application>psql</application>'s standard input,
        either using <application>echo</application> as illustrated above, or
        via a shell here-document, for example:
 <programlisting>
@@ -3570,10 +3563,6 @@ select 1\; select 2\; select 3;
         commands included in the string to divide it into multiple
         transactions.  (See <xref linkend="protocol-flow-multi-statement"/>
         for more details about how the server handles multi-query strings.)
-        <application>psql</application> prints only the last query result
-        it receives for each request; in this example, although all
-        three <command>SELECT</command>s are indeed executed, <application>psql</application>
-        only prints the <literal>3</literal>.
         </para>
         </listitem>
       </varlistentry>
@@ -4160,6 +4149,18 @@ bar
       </varlistentry>
 
       <varlistentry>
+        <term><varname>SHOW_ALL_RESULTS</varname></term>
+        <listitem>
+        <para>
+        When this variable is set to <literal>off</literal>, only the last
+        result of a combined query (<literal>\;</literal>) is shown instead of
+        all of them.  The default is <literal>on</literal>.  The off behavior
+        is for compatibility with older versions of psql.
+        </para>
+        </listitem>
+      </varlistentry>
+
+       <varlistentry>
         <term><varname>SHOW_CONTEXT</varname></term>
         <listitem>
         <para>