Introduce a SQL-callable function array_sort(anyarray).

Create a function that will sort the elements of an array
according to the element type's sort order.  If the array
has more than one dimension, the sub-arrays of the first
dimension are sorted per normal array-comparison rules,
leaving their contents alone.

Author: Junwang Zhao <zhjwpku@gmail.com>
Co-authored-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Discussion: https://postgr.es/m/CAEG8a3J41a4dpw_-F94fF-JPRXYxw-GfsgoGotKcjs9LVfEEvw@mail.gmail.com

Author: 2 people

doc/src/sgml/func.sgml

@@ -20741,6 +20741,42 @@ SELECT NULLIF(value, '(none)') ...
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>array_sort</primary>
+        </indexterm>
+        <function>array_sort</function> (
+          <parameter>array</parameter> <type>anyarray</type>
+          <optional>, <parameter>descending</parameter> <type>boolean</type>
+          <optional>, <parameter>nulls_first</parameter> <type>boolean</type>
+          </optional></optional> )
+        <returnvalue>anyarray</returnvalue>
+       </para>
+       <para>
+        Sorts the first dimension of the array.
+        The sort order is determined by the default sort ordering of the
+        array's element type; however, if the element type is collatable,
+        the collation to use can be forced by adding
+        a <literal>COLLATE</literal> clause to
+        the <parameter>array</parameter> argument.
+       </para>
+       <para>
+        If <parameter>descending</parameter> is true then sort in
+        descending order, otherwise ascending order.  If omitted, the
+        default is ascending order.
+        If <parameter>nulls_first</parameter> is true then nulls appear
+        before non-null values, otherwise nulls appear after non-null
+        values.
+        If omitted, <parameter>nulls_first</parameter> is taken to have
+        the same value as <parameter>descending</parameter>.
+       </para>
+       <para>
+        <literal>array_sort(ARRAY[[2,4],[2,1],[6,5]])</literal>
+        <returnvalue>{{2,1},{2,4},{6,5}}</returnvalue>
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm id="function-array-to-string">

src/backend/utils/adt/array_userfuncs.c

@@ -12,16 +12,19 @@
  */
 #include "postgres.h"
 
+#include "catalog/pg_operator_d.h"
 #include "catalog/pg_type.h"
 #include "common/int.h"
 #include "common/pg_prng.h"
 #include "libpq/pqformat.h"
+#include "miscadmin.h"
 #include "nodes/supportnodes.h"
 #include "port/pg_bitutils.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
 #include "utils/lsyscache.h"
+#include "utils/tuplesort.h"
 #include "utils/typcache.h"
 
 /*
@@ -43,6 +46,18 @@ typedef struct DeserialIOData
 	Oid			typioparam;
 } DeserialIOData;
 
+/*
+ * ArraySortCachedInfo
+ *		Used for caching catalog data in array_sort
+ */
+typedef struct ArraySortCachedInfo
+{
+	ArrayMetaState array_meta;	/* metadata for array_create_iterator */
+	Oid			elem_lt_opr;	/* "<" operator for element type */
+	Oid			elem_gt_opr;	/* ">" operator for element type */
+	Oid			array_type;		/* pg_type OID of array type */
+} ArraySortCachedInfo;
+
 static Datum array_position_common(FunctionCallInfo fcinfo);
 
 
@@ -1858,3 +1873,171 @@ array_reverse(PG_FUNCTION_ARGS)
 
 	PG_RETURN_ARRAYTYPE_P(result);
 }
+
+/*
+ * array_sort
+ *
+ * Sorts the first dimension of the array.
+ */
+static ArrayType *
+array_sort_internal(ArrayType *array, bool descending, bool nulls_first,
+					FunctionCallInfo fcinfo)
+{
+	ArrayType  *newarray;
+	Oid			collation = PG_GET_COLLATION();
+	int			ndim,
+			   *dims,
+			   *lbs;
+	ArraySortCachedInfo *cache_info;
+	Oid			elmtyp;
+	Oid			sort_typ;
+	Oid			sort_opr;
+	Tuplesortstate *tuplesortstate;
+	ArrayIterator array_iterator;
+	Datum		value;
+	bool		isnull;
+	ArrayBuildStateAny *astate = NULL;
+
+	ndim = ARR_NDIM(array);
+	dims = ARR_DIMS(array);
+	lbs = ARR_LBOUND(array);
+
+	/* Quick exit if we don't need to sort */
+	if (ndim < 1 || dims[0] < 2)
+		return array;
+
+	/* Set up cache area if we didn't already */
+	cache_info = (ArraySortCachedInfo *) fcinfo->flinfo->fn_extra;
+	if (cache_info == NULL)
+	{
+		cache_info = (ArraySortCachedInfo *)
+			MemoryContextAllocZero(fcinfo->flinfo->fn_mcxt,
+								   sizeof(ArraySortCachedInfo));
+		fcinfo->flinfo->fn_extra = cache_info;
+	}
+
+	/* Fetch and cache required data if we don't have it */
+	elmtyp = ARR_ELEMTYPE(array);
+	if (elmtyp != cache_info->array_meta.element_type)
+	{
+		TypeCacheEntry *typentry;
+
+		typentry = lookup_type_cache(elmtyp,
+									 TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
+		cache_info->array_meta.element_type = elmtyp;
+		cache_info->array_meta.typlen = typentry->typlen;
+		cache_info->array_meta.typbyval = typentry->typbyval;
+		cache_info->array_meta.typalign = typentry->typalign;
+		cache_info->elem_lt_opr = typentry->lt_opr;
+		cache_info->elem_gt_opr = typentry->gt_opr;
+		/* For some reason the typcache doesn't track array type */
+		cache_info->array_type = InvalidOid;
+	}
+
+	/* Identify the sort operator to use */
+	if (ndim == 1)
+	{
+		/* Need to sort the element type */
+		sort_typ = elmtyp;
+		sort_opr = (descending ? cache_info->elem_gt_opr : cache_info->elem_lt_opr);
+	}
+	else
+	{
+		/* Otherwise we're sorting arrays */
+		if (!OidIsValid(cache_info->array_type))
+		{
+			cache_info->array_type = get_array_type(elmtyp);
+			if (!OidIsValid(cache_info->array_type))
+				ereport(ERROR,
+						(errcode(ERRCODE_UNDEFINED_OBJECT),
+						 errmsg("could not find array type for data type %s",
+								format_type_be(elmtyp))));
+		}
+		sort_typ = cache_info->array_type;
+		/* We know what operators to use for arrays */
+		sort_opr = (descending ? ARRAY_GT_OP : ARRAY_LT_OP);
+	}
+
+	/*
+	 * Fail if we don't know how to sort.  The error message is chosen to
+	 * match what array_lt()/array_gt() will say in the multidimensional case.
+	 */
+	if (!OidIsValid(sort_opr))
+		ereport(ERROR,
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("could not identify a comparison function for type %s",
+					   format_type_be(elmtyp)));
+
+	/* Put the things to be sorted (elements or sub-arrays) into a tuplesort */
+	tuplesortstate = tuplesort_begin_datum(sort_typ,
+										   sort_opr,
+										   collation,
+										   nulls_first,
+										   work_mem,
+										   NULL,
+										   TUPLESORT_NONE);
+
+	array_iterator = array_create_iterator(array, ndim - 1,
+										   &cache_info->array_meta);
+	while (array_iterate(array_iterator, &value, &isnull))
+	{
+		tuplesort_putdatum(tuplesortstate, value, isnull);
+	}
+	array_free_iterator(array_iterator);
+
+	/* Do the sort */
+	tuplesort_performsort(tuplesortstate);
+
+	/* Extract results into a new array */
+	while (tuplesort_getdatum(tuplesortstate, true, false, &value, &isnull, NULL))
+	{
+		astate = accumArrayResultAny(astate, value, isnull,
+									 sort_typ, CurrentMemoryContext);
+	}
+	tuplesort_end(tuplesortstate);
+
+	newarray = DatumGetArrayTypeP(makeArrayResultAny(astate,
+													 CurrentMemoryContext,
+													 true));
+
+	/* Adjust lower bound to match the input */
+	ARR_LBOUND(newarray)[0] = lbs[0];
+
+	return newarray;
+}
+
+Datum
+array_sort(PG_FUNCTION_ARGS)
+{
+	ArrayType  *array = PG_GETARG_ARRAYTYPE_P(0);
+
+	PG_RETURN_ARRAYTYPE_P(array_sort_internal(array,
+											  false,
+											  false,
+											  fcinfo));
+}
+
+Datum
+array_sort_order(PG_FUNCTION_ARGS)
+{
+	ArrayType  *array = PG_GETARG_ARRAYTYPE_P(0);
+	bool		descending = PG_GETARG_BOOL(1);
+
+	PG_RETURN_ARRAYTYPE_P(array_sort_internal(array,
+											  descending,
+											  descending,
+											  fcinfo));
+}
+
+Datum
+array_sort_order_nulls_first(PG_FUNCTION_ARGS)
+{
+	ArrayType  *array = PG_GETARG_ARRAYTYPE_P(0);
+	bool		descending = PG_GETARG_BOOL(1);
+	bool		nulls_first = PG_GETARG_BOOL(2);
+
+	PG_RETURN_ARRAYTYPE_P(array_sort_internal(array,
+											  descending,
+											  nulls_first,
+											  fcinfo));
+}

src/include/catalog/pg_proc.dat

@@ -1772,6 +1772,18 @@
 { oid => '8686', descr => 'reverse array',
   proname => 'array_reverse', prorettype => 'anyarray',
   proargtypes => 'anyarray', prosrc => 'array_reverse' },
+{ oid => '8810', descr => 'sort array',
+  proname => 'array_sort', prorettype => 'anyarray', proargtypes => 'anyarray',
+  prosrc => 'array_sort' },
+{ oid => '8811', descr => 'sort array',
+  proname => 'array_sort', prorettype => 'anyarray',
+  proargtypes => 'anyarray bool', proargnames => '{array,descending}',
+  prosrc => 'array_sort_order' },
+{ oid => '8812', descr => 'sort array',
+  proname => 'array_sort', prorettype => 'anyarray',
+  proargtypes => 'anyarray bool bool',
+  proargnames => '{array,descending,nulls_first}',
+  prosrc => 'array_sort_order_nulls_first' },
 { oid => '3816', descr => 'array typanalyze',
   proname => 'array_typanalyze', provolatile => 's', prorettype => 'bool',
   proargtypes => 'internal', prosrc => 'array_typanalyze' },