[CF 6017] Add error_on_null() to produce an error if the input is null

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https://commitfest.postgresql.org/patch/6017

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Patch(es): https://www.postgresql.org/message-id/[email protected]
Author(s): Joel Jacobson

Author: Commitfest Bot

doc/src/sgml/func/func-comparison.sgml

@@ -631,6 +631,26 @@ SELECT NOT(ROW(table.*) IS NOT NULL) FROM TABLE; -- detect at least one null in
         <returnvalue>1</returnvalue>
        </para></entry>
       </row>
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>error_on_null</primary>
+        </indexterm>
+        <function>error_on_null</function> ( <type>anyelement</type> )
+        <returnvalue>anyelement | error</returnvalue>
+       </para>
+       <para>
+        Produces an error if the input is null, and returns the input otherwise.
+       </para>
+       <para>
+        <literal>error_on_null(42)</literal>
+        <returnvalue>42</returnvalue>
+       </para>
+       <para>
+        <literal>error_on_null(null)</literal>
+        <returnvalue>does not return</returnvalue>
+       </para></entry>
+      </row>
      </tbody>
     </tgroup>
    </table>

src/backend/utils/adt/misc.c

@@ -185,6 +185,21 @@ pg_num_nonnulls(PG_FUNCTION_ARGS)
 	PG_RETURN_INT32(nargs - nulls);
 }
 
+/*
+ * error_on_null()
+ *	Produces an error if the input is null, and returns the input otherwise
+ */
+Datum
+error_on_null(PG_FUNCTION_ARGS)
+{
+	if (PG_ARGISNULL(0))
+		ereport(ERROR,
+				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+				 errmsg("null value not allowed")));
+
+	PG_RETURN_DATUM(PG_GETARG_DATUM(0));
+}
+
 
 /*
  * current_database()

src/include/catalog/pg_proc.dat

@@ -12518,6 +12518,9 @@
 { oid => '6292', descr => 'aggregate transition function',
   proname => 'any_value_transfn', prorettype => 'anyelement',
   proargtypes => 'anyelement anyelement', prosrc => 'any_value_transfn' },
+{ oid => '8488', descr => 'error on null input; otherwise returns input unchanged',
+  proname => 'error_on_null', proisstrict => 'f', prorettype => 'anyelement',
+  proargtypes => 'anyelement', prosrc => 'error_on_null' },
 
 { oid => '6321', descr => 'list of available WAL summary files',
   proname => 'pg_available_wal_summaries', prorows => '100', proretset => 't',

src/test/regress/expected/misc_functions.out

@@ -177,6 +177,23 @@ ERROR:  function num_nulls() does not exist
 LINE 1: SELECT num_nulls();
                ^
 HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
+--
+-- error_on_null()
+--
+SELECT error_on_null(1);
+ error_on_null 
+---------------
+             1
+(1 row)
+
+SELECT error_on_null(NULL::int);
+ERROR:  null value not allowed
+SELECT error_on_null(ROW(1,NULL::int));
+ error_on_null 
+---------------
+ (1,)
+(1 row)
+
 --
 -- canonicalize_path()
 --

src/test/regress/sql/misc_functions.sql

@@ -77,6 +77,14 @@ SELECT num_nulls(VARIADIC '{}'::int[]);
 SELECT num_nonnulls();
 SELECT num_nulls();
 
+--
+-- error_on_null()
+--
+
+SELECT error_on_null(1);
+SELECT error_on_null(NULL::int);
+SELECT error_on_null(ROW(1,NULL::int));
+
 --
 -- canonicalize_path()
 --