SQL/JSON: Improve some error messages

This improves some error messages emitted by SQL/JSON query functions
by mentioning column name when available, such as when they are
invoked as part of evaluating JSON_TABLE() columns.  To do so, a new
field column_name is added to both JsonFuncExpr and JsonExpr that is
only populated when creating those nodes for transformed JSON_TABLE()
columns.

While at it, relevant error messages are reworded for clarity.

Reported-by: Jian He <[email protected]>
Suggested-by: Jian He <[email protected]>
Discussion: https://postgr.es/m/CACJufxG_e0QLCgaELrr2ZNz7AxPeGCNKAORe3fHtFCQLsH4J4Q@mail.gmail.com

4 files changed, 62 insertions, 37 deletions

diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index 41af28cb1eb..852186312c5 100644
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -4312,7 +4312,8 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 		case JSON_QUERY_OP:
 			*op->resvalue = JsonPathQuery(item, path, jsexpr->wrapper, &empty,
 										  !throw_error ? &error : NULL,
-										  jsestate->args);
+										  jsestate->args,
+										  jsexpr->column_name);
 
 			*op->resnull = (DatumGetPointer(*op->resvalue) == NULL);
 
@@ -4337,7 +4338,8 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 			{
 				JsonbValue *jbv = JsonPathValue(item, path, &empty,
 												!throw_error ? &error : NULL,
-												jsestate->args);
+												jsestate->args,
+												jsexpr->column_name);
 
 				if (jbv == NULL)
 				{
@@ -4407,30 +4409,33 @@ ExecEvalJsonExprPath(ExprState *state, ExprEvalStep *op,
 	/* Handle ON EMPTY. */
 	if (empty)
 	{
+		*op->resvalue = (Datum) 0;
+		*op->resnull = true;
 		if (jsexpr->on_empty)
 		{
-			if (jsexpr->on_empty->btype == JSON_BEHAVIOR_ERROR)
-				ereport(ERROR,
-						errcode(ERRCODE_NO_SQL_JSON_ITEM),
-						errmsg("no SQL/JSON item"));
-			else
+			if (jsexpr->on_empty->btype != JSON_BEHAVIOR_ERROR)
+			{
 				jsestate->empty.value = BoolGetDatum(true);
-
-			Assert(jsestate->jump_empty >= 0);
-			return jsestate->jump_empty;
+				Assert(jsestate->jump_empty >= 0);
+				return jsestate->jump_empty;
+			}
+		}
+		else if (jsexpr->on_error->btype != JSON_BEHAVIOR_ERROR)
+		{
+			jsestate->error.value = BoolGetDatum(true);
+			Assert(!throw_error && jsestate->jump_error >= 0);
+			return jsestate->jump_error;
 		}
-		else if (jsexpr->on_error->btype == JSON_BEHAVIOR_ERROR)
+
+		if (jsexpr->column_name)
 			ereport(ERROR,
 					errcode(ERRCODE_NO_SQL_JSON_ITEM),
-					errmsg("no SQL/JSON item"));
+					errmsg("no SQL/JSON item found for specified path of column \"%s\"",
+						   jsexpr->column_name));
 		else
-			jsestate->error.value = BoolGetDatum(true);
-
-		*op->resvalue = (Datum) 0;
-		*op->resnull = true;
-
-		Assert(!throw_error && jsestate->jump_error >= 0);
-		return jsestate->jump_error;
+			ereport(ERROR,
+					errcode(ERRCODE_NO_SQL_JSON_ITEM),
+					errmsg("no SQL/JSON item found for specified path"));
 	}
 
 	/*
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 4c98d7a046c..34ac17868b5 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -4311,6 +4311,7 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
 	jsexpr = makeNode(JsonExpr);
 	jsexpr->location = func->location;
 	jsexpr->op = func->op;
+	jsexpr->column_name = func->column_name;
 
 	/*
 	 * jsonpath machinery can only handle jsonb documents, so coerce the input
diff --git a/src/backend/parser/parse_jsontable.c b/src/backend/parser/parse_jsontable.c
index 99d3101f6b2..37f2cba0ef0 100644
--- a/src/backend/parser/parse_jsontable.c
+++ b/src/backend/parser/parse_jsontable.c
@@ -402,12 +402,6 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	Node	   *pathspec;
 	JsonFuncExpr *jfexpr = makeNode(JsonFuncExpr);
 
-	/*
-	 * XXX consider inventing JSON_TABLE_VALUE_OP, etc. and pass the column
-	 * name via JsonExpr so that JsonPathValue(), etc. can provide error
-	 * message tailored to JSON_TABLE(), such as by mentioning the column
-	 * names in the message.
-	 */
 	if (jtc->coltype == JTC_REGULAR)
 		jfexpr->op = JSON_VALUE_OP;
 	else if (jtc->coltype == JTC_EXISTS)
@@ -415,6 +409,10 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	else
 		jfexpr->op = JSON_QUERY_OP;
 
+	/* Pass the column name so any runtime JsonExpr errors can print it. */
+	Assert(jtc->name != NULL);
+	jfexpr->column_name = pstrdup(jtc->name);
+
 	jfexpr->context_item = makeJsonValueExpr((Expr *) contextItemExpr, NULL,
 											 makeJsonFormat(JS_FORMAT_DEFAULT,
 															JS_ENC_DEFAULT,
diff --git a/src/backend/utils/adt/jsonpath_exec.c b/src/backend/utils/adt/jsonpath_exec.c
index 103572ed932..e74dc1b2d42 100644
--- a/src/backend/utils/adt/jsonpath_exec.c
+++ b/src/backend/utils/adt/jsonpath_exec.c
@@ -3899,7 +3899,8 @@ JsonPathExists(Datum jb, JsonPath *jp, bool *error, List *vars)
  */
 Datum
 JsonPathQuery(Datum jb, JsonPath *jp, JsonWrapper wrapper, bool *empty,
-			  bool *error, List *vars)
+			  bool *error, List *vars,
+			  const char *column_name)
 {
 	JsonbValue *singleton;
 	bool		wrap;
@@ -3950,10 +3951,17 @@ JsonPathQuery(Datum jb, JsonPath *jp, JsonWrapper wrapper, bool *empty,
 			return (Datum) 0;
 		}
 
-		ereport(ERROR,
-				(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
-				 errmsg("JSON path expression in JSON_QUERY should return singleton item without wrapper"),
-				 errhint("Use WITH WRAPPER clause to wrap SQL/JSON item sequence into array.")));
+		if (column_name)
+			ereport(ERROR,
+					(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
+					 errmsg("JSON path expression for column \"%s\" should return single item without wrapper",
+							column_name),
+					 errhint("Use WITH WRAPPER clause to wrap SQL/JSON items into array.")));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
+					 errmsg("JSON path expression in JSON_QUERY should return single item without wrapper"),
+					 errhint("Use WITH WRAPPER clause to wrap SQL/JSON items into array.")));
 	}
 
 	if (singleton)
@@ -3970,7 +3978,8 @@ JsonPathQuery(Datum jb, JsonPath *jp, JsonWrapper wrapper, bool *empty,
  * *error to true.  *empty is set to true if no match is found.
  */
 JsonbValue *
-JsonPathValue(Datum jb, JsonPath *jp, bool *empty, bool *error, List *vars)
+JsonPathValue(Datum jb, JsonPath *jp, bool *empty, bool *error, List *vars,
+			  const char *column_name)
 {
 	JsonbValue *res;
 	JsonValueList found = {0};
@@ -4006,9 +4015,15 @@ JsonPathValue(Datum jb, JsonPath *jp, bool *empty, bool *error, List *vars)
 			return NULL;
 		}
 
-		ereport(ERROR,
-				(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
-				 errmsg("JSON path expression in JSON_VALUE should return singleton scalar item")));
+		if (column_name)
+			ereport(ERROR,
+					(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
+					 errmsg("JSON path expression for column \"%s\" should return single scalar item",
+							column_name)));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_MORE_THAN_ONE_SQL_JSON_ITEM),
+					 errmsg("JSON path expression in JSON_VALUE should return single scalar item")));
 	}
 
 	res = JsonValueListHead(&found);
@@ -4024,9 +4039,15 @@ JsonPathValue(Datum jb, JsonPath *jp, bool *empty, bool *error, List *vars)
 			return NULL;
 		}
 
-		ereport(ERROR,
-				(errcode(ERRCODE_SQL_JSON_SCALAR_REQUIRED),
-				 errmsg("JSON path expression in JSON_VALUE should return singleton scalar item")));
+		if (column_name)
+			ereport(ERROR,
+					(errcode(ERRCODE_SQL_JSON_SCALAR_REQUIRED),
+					 errmsg("JSON path expression for column \"%s\" should return single scalar item",
+							column_name)));
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_SQL_JSON_SCALAR_REQUIRED),
+					 errmsg("JSON path expression in JSON_VALUE should return single scalar item")));
 	}
 
 	if (res->type == jbvNull)