Add SQL/JSON query functions

This introduces the following SQL/JSON functions for querying JSON
data using jsonpath expressions:

JSON_EXISTS(), which can be used to apply a jsonpath expression to a
JSON value to check if it yields any values.

JSON_QUERY(), which can be used to to apply a jsonpath expression to
a JSON value to get a JSON object, an array, or a string.  There are
various options to control whether multi-value result uses array
wrappers and whether the singleton scalar strings are quoted or not.

JSON_VALUE(), which can be used to apply a jsonpath expression to a
JSON value to return a single scalar value, producing an error if it
multiple values are matched.

Both JSON_VALUE() and JSON_QUERY() functions have options for
handling EMPTY and ERROR conditions, which can be used to specify
the behavior when no values are matched and when an error occurs
during jsonpath evaluation, respectively.

Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Andrew Dunstan <andrew@dunslane.net>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Peter Eisentraut <peter@eisentraut.org>
Author: Jian He <jian.universality@gmail.com>

Reviewers have included (in no particular order):

Andres Freund, Alexander Korotkov, Pavel Stehule, Andrew Alsup,
Erik Rijkers, Zihong Yu, Himanshu Upadhyaya, Daniel Gustafsson,
Justin Pryzby, Álvaro Herrera, Jian He, Anton A. Melnikov,
Nikita Malakhov, Peter Eisentraut, Tomas Vondra

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
Discussion: https://postgr.es/m/CA+HiwqHROpf9e644D8BRqYvaAPmgBZVup-xKMDPk-nd4EpgzHw@mail.gmail.com
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com

1 files changed, 138 insertions, 0 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 07b454418d7..4a7402e09ef 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -478,6 +478,8 @@ static void get_const_expr(Const *constval, deparse_context *context,
 						   int showtype);
 static void get_const_collation(Const *constval, deparse_context *context);
 static void get_json_format(JsonFormat *format, StringInfo buf);
+static void get_json_returning(JsonReturning *returning, StringInfo buf,
+							   bool json_format_by_default);
 static void get_json_constructor(JsonConstructorExpr *ctor,
 								 deparse_context *context, bool showimplicit);
 static void get_json_constructor_options(JsonConstructorExpr *ctor,
@@ -520,6 +522,8 @@ static char *generate_qualified_type_name(Oid typid);
 static text *string_to_text(char *str);
 static char *flatten_reloptions(Oid relid);
 static void get_reloptions(StringInfo buf, Datum reloptions);
+static void get_json_path_spec(Node *path_spec, deparse_context *context,
+							   bool showimplicit);
 
 #define only_marker(rte)  ((rte)->inh ? "" : "ONLY ")
 
@@ -8466,6 +8470,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 		case T_MergeSupportFunc:
 		case T_FuncExpr:
 		case T_JsonConstructorExpr:
+		case T_JsonExpr:
 			/* function-like: name(..) or name[..] */
 			return true;
 
@@ -8637,6 +8642,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				case T_GroupingFunc:	/* own parentheses */
 				case T_WindowFunc:	/* own parentheses */
 				case T_CaseExpr:	/* other separators */
+				case T_JsonExpr:	/* own parentheses */
 					return true;
 				default:
 					return false;
@@ -8752,6 +8758,64 @@ get_rule_expr_paren(Node *node, deparse_context *context,
 		appendStringInfoChar(context->buf, ')');
 }
 
+static void
+get_json_behavior(JsonBehavior *behavior, deparse_context *context,
+				  const char *on)
+{
+	/*
+	 * The order of array elements must correspond to the order of
+	 * JsonBehaviorType members.
+	 */
+	const char *behavior_names[] =
+	{
+		" NULL",
+		" ERROR",
+		" EMPTY",
+		" TRUE",
+		" FALSE",
+		" UNKNOWN",
+		" EMPTY ARRAY",
+		" EMPTY OBJECT",
+		" DEFAULT "
+	};
+
+	if ((int) behavior->btype < 0 || behavior->btype >= lengthof(behavior_names))
+		elog(ERROR, "invalid json behavior type: %d", behavior->btype);
+
+	appendStringInfoString(context->buf, behavior_names[behavior->btype]);
+
+	if (behavior->btype == JSON_BEHAVIOR_DEFAULT)
+		get_rule_expr(behavior->expr, context, false);
+
+	appendStringInfo(context->buf, " ON %s", on);
+}
+
+/*
+ * get_json_expr_options
+ *
+ * Parse back common options for JSON_QUERY, JSON_VALUE, JSON_EXISTS.
+ */
+static void
+get_json_expr_options(JsonExpr *jsexpr, deparse_context *context,
+					  JsonBehaviorType default_behavior)
+{
+	if (jsexpr->op == JSON_QUERY_OP)
+	{
+		if (jsexpr->wrapper == JSW_CONDITIONAL)
+			appendStringInfo(context->buf, " WITH CONDITIONAL WRAPPER");
+		else if (jsexpr->wrapper == JSW_UNCONDITIONAL)
+			appendStringInfo(context->buf, " WITH UNCONDITIONAL WRAPPER");
+
+		if (jsexpr->omit_quotes)
+			appendStringInfo(context->buf, " OMIT QUOTES");
+	}
+
+	if (jsexpr->on_empty && jsexpr->on_empty->btype != default_behavior)
+		get_json_behavior(jsexpr->on_empty, context, "EMPTY");
+
+	if (jsexpr->on_error && jsexpr->on_error->btype != default_behavior)
+		get_json_behavior(jsexpr->on_error, context, "ERROR");
+}
 
 /* ----------
  * get_rule_expr			- Parse back an expression
@@ -10031,6 +10095,67 @@ get_rule_expr(Node *node, deparse_context *context,
 			}
 			break;
 
+		case T_JsonExpr:
+			{
+				JsonExpr   *jexpr = (JsonExpr *) node;
+
+				switch (jexpr->op)
+				{
+					case JSON_EXISTS_OP:
+						appendStringInfoString(buf, "JSON_EXISTS(");
+						break;
+					case JSON_QUERY_OP:
+						appendStringInfoString(buf, "JSON_QUERY(");
+						break;
+					case JSON_VALUE_OP:
+						appendStringInfoString(buf, "JSON_VALUE(");
+						break;
+					default:
+						elog(ERROR, "unrecognized JsonExpr op: %d",
+							 (int) jexpr->op);
+				}
+
+				get_rule_expr(jexpr->formatted_expr, context, showimplicit);
+
+				appendStringInfoString(buf, ", ");
+
+				get_json_path_spec(jexpr->path_spec, context, showimplicit);
+
+				if (jexpr->passing_values)
+				{
+					ListCell   *lc1,
+							   *lc2;
+					bool		needcomma = false;
+
+					appendStringInfoString(buf, " PASSING ");
+
+					forboth(lc1, jexpr->passing_names,
+							lc2, jexpr->passing_values)
+					{
+						if (needcomma)
+							appendStringInfoString(buf, ", ");
+						needcomma = true;
+
+						get_rule_expr((Node *) lfirst(lc2), context, showimplicit);
+						appendStringInfo(buf, " AS %s",
+										 ((String *) lfirst_node(String, lc1))->sval);
+					}
+				}
+
+				if (jexpr->op != JSON_EXISTS_OP ||
+					jexpr->returning->typid != BOOLOID)
+					get_json_returning(jexpr->returning, context->buf,
+									   jexpr->op == JSON_QUERY_OP);
+
+				get_json_expr_options(jexpr, context,
+									  jexpr->op != JSON_EXISTS_OP ?
+									  JSON_BEHAVIOR_NULL :
+									  JSON_BEHAVIOR_FALSE);
+
+				appendStringInfoString(buf, ")");
+			}
+			break;
+
 		case T_List:
 			{
 				char	   *sep;
@@ -10154,6 +10279,7 @@ looks_like_function(Node *node)
 		case T_MinMaxExpr:
 		case T_SQLValueFunction:
 		case T_XmlExpr:
+		case T_JsonExpr:
 			/* these are all accepted by func_expr_common_subexpr */
 			return true;
 		default:
@@ -11024,6 +11150,18 @@ get_const_collation(Const *constval, deparse_context *context)
 }
 
 /*
+ * get_json_path_spec		- Parse back a JSON path specification
+ */
+static void
+get_json_path_spec(Node *path_spec, deparse_context *context, bool showimplicit)
+{
+	if (IsA(path_spec, Const))
+		get_const_expr((Const *) path_spec, context, -1);
+	else
+		get_rule_expr(path_spec, context, showimplicit);
+}
+
+/*
  * get_json_format			- Parse back a JsonFormat node
  */
 static void