Add num_nulls() and num_nonnulls() to count NULL arguments.

An example use-case is "CHECK(num_nonnulls(a,b,c) = 1)" to assert that
exactly one of a,b,c isn't NULL.  The functions are variadic, so they
can also be pressed into service to count the number of null or nonnull
elements in an array.

Marko Tiikkaja, reviewed by Pavel Stehule

src/test/regress/expected/misc_functions.out

@@ -0,0 +1,135 @@
+--
+-- num_nulls()
+--
+SELECT num_nonnulls(NULL);
+ num_nonnulls 
+--------------
+            0
+(1 row)
+
+SELECT num_nonnulls('1');
+ num_nonnulls 
+--------------
+            1
+(1 row)
+
+SELECT num_nonnulls(NULL::text);
+ num_nonnulls 
+--------------
+            0
+(1 row)
+
+SELECT num_nonnulls(NULL::text, NULL::int);
+ num_nonnulls 
+--------------
+            0
+(1 row)
+
+SELECT num_nonnulls(1, 2, NULL::text, NULL::point, '', int8 '9', 1.0 / NULL);
+ num_nonnulls 
+--------------
+            4
+(1 row)
+
+SELECT num_nonnulls(VARIADIC '{1,2,NULL,3}'::int[]);
+ num_nonnulls 
+--------------
+            3
+(1 row)
+
+SELECT num_nonnulls(VARIADIC '{"1","2","3","4"}'::text[]);
+ num_nonnulls 
+--------------
+            4
+(1 row)
+
+SELECT num_nonnulls(VARIADIC ARRAY(SELECT CASE WHEN i <> 40 THEN i END FROM generate_series(1, 100) i));
+ num_nonnulls 
+--------------
+           99
+(1 row)
+
+SELECT num_nulls(NULL);
+ num_nulls 
+-----------
+         1
+(1 row)
+
+SELECT num_nulls('1');
+ num_nulls 
+-----------
+         0
+(1 row)
+
+SELECT num_nulls(NULL::text);
+ num_nulls 
+-----------
+         1
+(1 row)
+
+SELECT num_nulls(NULL::text, NULL::int);
+ num_nulls 
+-----------
+         2
+(1 row)
+
+SELECT num_nulls(1, 2, NULL::text, NULL::point, '', int8 '9', 1.0 / NULL);
+ num_nulls 
+-----------
+         3
+(1 row)
+
+SELECT num_nulls(VARIADIC '{1,2,NULL,3}'::int[]);
+ num_nulls 
+-----------
+         1
+(1 row)
+
+SELECT num_nulls(VARIADIC '{"1","2","3","4"}'::text[]);
+ num_nulls 
+-----------
+         0
+(1 row)
+
+SELECT num_nulls(VARIADIC ARRAY(SELECT CASE WHEN i <> 40 THEN i END FROM generate_series(1, 100) i));
+ num_nulls 
+-----------
+         1
+(1 row)
+
+-- special cases
+SELECT num_nonnulls(VARIADIC NULL::text[]);
+ num_nonnulls 
+--------------
+             
+(1 row)
+
+SELECT num_nonnulls(VARIADIC '{}'::int[]);
+ num_nonnulls 
+--------------
+            0
+(1 row)
+
+SELECT num_nulls(VARIADIC NULL::text[]);
+ num_nulls 
+-----------
+          
+(1 row)
+
+SELECT num_nulls(VARIADIC '{}'::int[]);
+ num_nulls 
+-----------
+         0
+(1 row)
+
+-- should fail, one or more arguments is required
+SELECT num_nonnulls();
+ERROR:  function num_nonnulls() does not exist
+LINE 1: SELECT num_nonnulls();
+               ^
+HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
+SELECT num_nulls();
+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.

src/test/regress/parallel_schedule

@@ -89,7 +89,7 @@ test: brin gin gist spgist privileges security_label collate matview lock replic
 # ----------
 # Another group of parallel tests
 # ----------
-test: alter_generic alter_operator misc psql async dbsize
+test: alter_generic alter_operator misc psql async dbsize misc_functions
 
 # rules cannot run concurrently with any test that creates a view
 test: rules

src/test/regress/serial_schedule

@@ -119,6 +119,7 @@ test: misc
 test: psql
 test: async
 test: dbsize
+test: misc_functions
 test: rules
 test: select_views
 test: portals_p2

src/test/regress/sql/misc_functions.sql

@@ -0,0 +1,31 @@
+--
+-- num_nulls()
+--
+
+SELECT num_nonnulls(NULL);
+SELECT num_nonnulls('1');
+SELECT num_nonnulls(NULL::text);
+SELECT num_nonnulls(NULL::text, NULL::int);
+SELECT num_nonnulls(1, 2, NULL::text, NULL::point, '', int8 '9', 1.0 / NULL);
+SELECT num_nonnulls(VARIADIC '{1,2,NULL,3}'::int[]);
+SELECT num_nonnulls(VARIADIC '{"1","2","3","4"}'::text[]);
+SELECT num_nonnulls(VARIADIC ARRAY(SELECT CASE WHEN i <> 40 THEN i END FROM generate_series(1, 100) i));
+
+SELECT num_nulls(NULL);
+SELECT num_nulls('1');
+SELECT num_nulls(NULL::text);
+SELECT num_nulls(NULL::text, NULL::int);
+SELECT num_nulls(1, 2, NULL::text, NULL::point, '', int8 '9', 1.0 / NULL);
+SELECT num_nulls(VARIADIC '{1,2,NULL,3}'::int[]);
+SELECT num_nulls(VARIADIC '{"1","2","3","4"}'::text[]);
+SELECT num_nulls(VARIADIC ARRAY(SELECT CASE WHEN i <> 40 THEN i END FROM generate_series(1, 100) i));
+
+-- special cases
+SELECT num_nonnulls(VARIADIC NULL::text[]);
+SELECT num_nonnulls(VARIADIC '{}'::int[]);
+SELECT num_nulls(VARIADIC NULL::text[]);
+SELECT num_nulls(VARIADIC '{}'::int[]);
+
+-- should fail, one or more arguments is required
+SELECT num_nonnulls();
+SELECT num_nulls();