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

Author: adunstan

src/backend/executor/execExpr.c

@@ -47,6 +47,7 @@
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/datum.h"
+#include "utils/jsonpath.h"
 #include "utils/lsyscache.h"
 #include "utils/typcache.h"
 
@@ -85,6 +86,40 @@ static void ExecBuildAggTransCall(ExprState *state, AggState *aggstate,
 								  bool nullcheck);
 
 
+static ExprState *
+ExecInitExprInternal(Expr *node, PlanState *parent, ParamListInfo ext_params,
+					 Datum *caseval, bool *casenull)
+{
+	ExprState  *state;
+	ExprEvalStep scratch = {0};
+
+	/* Special case: NULL expression produces a NULL ExprState pointer */
+	if (node == NULL)
+		return NULL;
+
+	/* Initialize ExprState with empty step list */
+	state = makeNode(ExprState);
+	state->expr = node;
+	state->parent = parent;
+	state->ext_params = ext_params;
+	state->innermost_caseval = caseval;
+	state->innermost_casenull = casenull;
+
+	/* Insert EEOP_*_FETCHSOME steps as needed */
+	ExecInitExprSlots(state, (Node *) node);
+
+	/* Compile the expression proper */
+	ExecInitExprRec(node, state, &state->resvalue, &state->resnull);
+
+	/* Finally, append a DONE step */
+	scratch.opcode = EEOP_DONE;
+	ExprEvalPushStep(state, &scratch);
+
+	ExecReadyExpr(state);
+
+	return state;
+}
+
 /*
  * ExecInitExpr: prepare an expression tree for execution
  *
@@ -122,32 +157,7 @@ static void ExecBuildAggTransCall(ExprState *state, AggState *aggstate,
 ExprState *
 ExecInitExpr(Expr *node, PlanState *parent)
 {
-	ExprState  *state;
-	ExprEvalStep scratch = {0};
-
-	/* Special case: NULL expression produces a NULL ExprState pointer */
-	if (node == NULL)
-		return NULL;
-
-	/* Initialize ExprState with empty step list */
-	state = makeNode(ExprState);
-	state->expr = node;
-	state->parent = parent;
-	state->ext_params = NULL;
-
-	/* Insert EEOP_*_FETCHSOME steps as needed */
-	ExecInitExprSlots(state, (Node *) node);
-
-	/* Compile the expression proper */
-	ExecInitExprRec(node, state, &state->resvalue, &state->resnull);
-
-	/* Finally, append a DONE step */
-	scratch.opcode = EEOP_DONE;
-	ExprEvalPushStep(state, &scratch);
-
-	ExecReadyExpr(state);
-
-	return state;
+	return ExecInitExprInternal(node, parent, NULL, NULL, NULL);
 }
 
 /*
@@ -159,32 +169,20 @@ ExecInitExpr(Expr *node, PlanState *parent)
 ExprState *
 ExecInitExprWithParams(Expr *node, ParamListInfo ext_params)
 {
-	ExprState  *state;
-	ExprEvalStep scratch = {0};
-
-	/* Special case: NULL expression produces a NULL ExprState pointer */
-	if (node == NULL)
-		return NULL;
-
-	/* Initialize ExprState with empty step list */
-	state = makeNode(ExprState);
-	state->expr = node;
-	state->parent = NULL;
-	state->ext_params = ext_params;
-
-	/* Insert EEOP_*_FETCHSOME steps as needed */
-	ExecInitExprSlots(state, (Node *) node);
-
-	/* Compile the expression proper */
-	ExecInitExprRec(node, state, &state->resvalue, &state->resnull);
-
-	/* Finally, append a DONE step */
-	scratch.opcode = EEOP_DONE;
-	ExprEvalPushStep(state, &scratch);
-
-	ExecReadyExpr(state);
+	return ExecInitExprInternal(node, NULL, ext_params, NULL, NULL);
+}
 
-	return state;
+/*
+ * ExecInitExprWithCaseValue: prepare an expression tree for execution
+ *
+ * This is the same as ExecInitExpr, except that a pointer to the value for
+ * CasTestExpr is passed here.
+ */
+ExprState *
+ExecInitExprWithCaseValue(Expr *node, PlanState *parent,
+						  Datum *caseval, bool *casenull)
+{
+	return ExecInitExprInternal(node, parent, NULL, caseval, casenull);
 }
 
 /*
@@ -2526,6 +2524,112 @@ ExecInitExprRec(Expr *node, ExprState *state,
 				break;
 			}
 
+		case T_JsonExpr:
+			{
+				JsonExpr   *jexpr = castNode(JsonExpr, node);
+				ListCell   *argexprlc;
+				ListCell   *argnamelc;
+
+				scratch.opcode = EEOP_JSONEXPR;
+				scratch.d.jsonexpr.jsexpr = jexpr;
+
+				scratch.d.jsonexpr.formatted_expr =
+					palloc(sizeof(*scratch.d.jsonexpr.formatted_expr));
+
+				ExecInitExprRec((Expr *) jexpr->formatted_expr, state,
+								&scratch.d.jsonexpr.formatted_expr->value,
+								&scratch.d.jsonexpr.formatted_expr->isnull);
+
+				scratch.d.jsonexpr.pathspec =
+					palloc(sizeof(*scratch.d.jsonexpr.pathspec));
+
+				ExecInitExprRec((Expr *) jexpr->path_spec, state,
+								&scratch.d.jsonexpr.pathspec->value,
+								&scratch.d.jsonexpr.pathspec->isnull);
+
+				scratch.d.jsonexpr.res_expr =
+					palloc(sizeof(*scratch.d.jsonexpr.res_expr));
+
+				scratch.d.jsonexpr.result_expr = jexpr->result_coercion
+					? ExecInitExprWithCaseValue((Expr *) jexpr->result_coercion->expr,
+												state->parent,
+												&scratch.d.jsonexpr.res_expr->value,
+												&scratch.d.jsonexpr.res_expr->isnull)
+					: NULL;
+
+				scratch.d.jsonexpr.default_on_empty = !jexpr->on_empty ? NULL :
+					ExecInitExpr((Expr *) jexpr->on_empty->default_expr,
+								 state->parent);
+
+				scratch.d.jsonexpr.default_on_error =
+					ExecInitExpr((Expr *) jexpr->on_error->default_expr,
+								 state->parent);
+
+				if (jexpr->omit_quotes ||
+					(jexpr->result_coercion && jexpr->result_coercion->via_io))
+				{
+					Oid			typinput;
+
+					/* lookup the result type's input function */
+					getTypeInputInfo(jexpr->returning->typid, &typinput,
+									 &scratch.d.jsonexpr.input.typioparam);
+					fmgr_info(typinput, &scratch.d.jsonexpr.input.func);
+				}
+
+				scratch.d.jsonexpr.args = NIL;
+
+				forboth(argexprlc, jexpr->passing_values,
+						argnamelc, jexpr->passing_names)
+				{
+					Expr	   *argexpr = (Expr *) lfirst(argexprlc);
+					String	   *argname = lfirst_node(String, argnamelc);
+					JsonPathVariableEvalContext *var = palloc(sizeof(*var));
+
+					var->name = pstrdup(argname->sval);
+					var->typid = exprType((Node *) argexpr);
+					var->typmod = exprTypmod((Node *) argexpr);
+					var->estate = ExecInitExpr(argexpr, state->parent);
+					var->econtext = NULL;
+					var->evaluated = false;
+					var->value = (Datum) 0;
+					var->isnull = true;
+
+					scratch.d.jsonexpr.args =
+						lappend(scratch.d.jsonexpr.args, var);
+				}
+
+				scratch.d.jsonexpr.cache = NULL;
+
+				if (jexpr->coercions)
+				{
+					JsonCoercion **coercion;
+					struct JsonCoercionState *cstate;
+					Datum	   *caseval;
+					bool	   *casenull;
+
+					scratch.d.jsonexpr.coercion_expr =
+						palloc(sizeof(*scratch.d.jsonexpr.coercion_expr));
+
+					caseval = &scratch.d.jsonexpr.coercion_expr->value;
+					casenull = &scratch.d.jsonexpr.coercion_expr->isnull;
+
+					for (cstate = &scratch.d.jsonexpr.coercions.null,
+						 coercion = &jexpr->coercions->null;
+						 coercion <= &jexpr->coercions->composite;
+						 coercion++, cstate++)
+					{
+						cstate->coercion = *coercion;
+						cstate->estate = *coercion ?
+							ExecInitExprWithCaseValue((Expr *)(*coercion)->expr,
+													  state->parent,
+													  caseval, casenull) : NULL;
+					}
+				}
+
+				ExprEvalPushStep(state, &scratch);
+				break;
+			}
+
 		default:
 			elog(ERROR, "unrecognized node type: %d",
 				 (int) nodeTag(node));