SQL/JSON query functions

This introduces the SQL/JSON functions for querying JSON data using
jsonpath expressions. The functions are:

JSON_EXISTS()
JSON_QUERY()
JSON_VALUE()

All of these functions only operate on jsonb. The workaround for now is
to cast the argument to jsonb.

JSON_EXISTS() tests if the jsonpath expression applied to the jsonb
value yields any values. JSON_VALUE() must return a single value, and an
error occurs if it tries to return multiple values. JSON_QUERY() must
return a json object or array, and there are various WRAPPER options for
handling scalar or multi-value results. Both these functions have
options for handling EMPTY and ERROR conditions.

Nikita Glukhov

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.

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru

1 files changed, 54 insertions, 0 deletions

diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index a41722ae1e4..240d07982ab 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -21,6 +21,7 @@
 struct ExprEvalStep;
 struct SubscriptingRefState;
 struct ScalarArrayOpExprHashTable;
+struct JsonbValue;
 
 /* Bits in ExprState->flags (see also execnodes.h for public flag bits): */
 /* expression's interpreter has been initialized */
@@ -241,6 +242,7 @@ typedef enum ExprEvalOp
 	EEOP_SUBPLAN,
 	EEOP_JSON_CONSTRUCTOR,
 	EEOP_IS_JSON,
+	EEOP_JSONEXPR,
 
 	/* aggregation related nodes */
 	EEOP_AGG_STRICT_DESERIALIZE,
@@ -687,6 +689,50 @@ typedef struct ExprEvalStep
 					JsonIsPredicate *pred;	/* original expression node */
 		}			is_json;
 
+		/* for EEOP_JSONEXPR */
+		struct
+		{
+			JsonExpr   *jsexpr;			/* original expression node */
+
+			struct
+			{
+				FmgrInfo	func;		/* typinput function for output type */
+				Oid			typioparam;
+			} input;					/* I/O info for output type */
+
+			NullableDatum
+					   *formatted_expr,		/* formatted context item value */
+					   *res_expr,			/* result item */
+					   *coercion_expr,		/* input for JSON item coercion */
+					   *pathspec;			/* path specification value */
+
+			ExprState  *result_expr;		/* coerced to output type */
+			ExprState  *default_on_empty;	/* ON EMPTY DEFAULT expression */
+			ExprState  *default_on_error;	/* ON ERROR DEFAULT expression */
+			List	   *args;				/* passing arguments */
+
+			void	   *cache;				/* cache for json_populate_type() */
+
+			struct JsonCoercionsState
+			{
+				struct JsonCoercionState
+				{
+					JsonCoercion *coercion;		/* coercion expression */
+					ExprState  *estate;	/* coercion expression state */
+				} 			null,
+							string,
+							numeric,
+							boolean,
+							date,
+							time,
+							timetz,
+							timestamp,
+							timestamptz,
+							composite;
+			}			coercions;	/* states for coercion from SQL/JSON item
+									 * types directly to the output type */
+		}			jsonexpr;
+
 	}			d;
 } ExprEvalStep;
 
@@ -791,6 +837,14 @@ extern void ExecEvalSysVar(ExprState *state, ExprEvalStep *op,
 						   ExprContext *econtext, TupleTableSlot *slot);
 extern void ExecEvalJsonConstructor(ExprState *state, ExprEvalStep *op,
 									ExprContext *econtext);
+extern void ExecEvalJson(ExprState *state, ExprEvalStep *op,
+						 ExprContext *econtext);
+extern Datum ExecPrepareJsonItemCoercion(struct JsonbValue *item,
+										 JsonReturning *returning,
+										 struct JsonCoercionsState *coercions,
+										 struct JsonCoercionState **pjcstate);
+extern bool ExecEvalJsonNeedsSubTransaction(JsonExpr *jsexpr,
+											struct JsonCoercionsState *);
 
 extern void ExecAggInitGroup(AggState *aggstate, AggStatePerTrans pertrans, AggStatePerGroup pergroup,
 							 ExprContext *aggcontext);