Support XMLTABLE query expression

XMLTABLE is defined by the SQL/XML standard as a feature that allows
turning XML-formatted data into relational form, so that it can be used
as a <table primary> in the FROM clause of a query.

This new construct provides significant simplicity and performance
benefit for XML data processing; what in a client-side custom
implementation was reported to take 20 minutes can be executed in 400ms
using XMLTABLE.  (The same functionality was said to take 10 seconds
using nested PostgreSQL XPath function calls, and 5 seconds using
XMLReader under PL/Python).

The implemented syntax deviates slightly from what the standard
requires.  First, the standard indicates that the PASSING clause is
optional and that multiple XML input documents may be given to it; we
make it mandatory and accept a single document only.  Second, we don't
currently support a default namespace to be specified.

This implementation relies on a new executor node based on a hardcoded
method table.  (Because the grammar is fixed, there is no extensibility
in the current approach; further constructs can be implemented on top of
this such as JSON_TABLE, but they require changes to core code.)

Author: Pavel Stehule, Álvaro Herrera
Extensively reviewed by: Craig Ringer
Discussion: https://postgr.es/m/CAFj8pRAgfzMD-LoSmnMGybD0WsEznLHWap8DO79+-GTRAPR4qA@mail.gmail.com

1 files changed, 91 insertions, 0 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index bb2a8a35865..b3eac06c50e 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -588,6 +588,27 @@ _copyFunctionScan(const FunctionScan *from)
 }
 
 /*
+ * _copyTableFuncScan
+ */
+static TableFuncScan *
+_copyTableFuncScan(const TableFuncScan *from)
+{
+	TableFuncScan *newnode = makeNode(TableFuncScan);
+
+	/*
+	 * copy node superclass fields
+	 */
+	CopyScanFields((const Scan *) from, (Scan *) newnode);
+
+	/*
+	 * copy remainder of node
+	 */
+	COPY_NODE_FIELD(tablefunc);
+
+	return newnode;
+}
+
+/*
  * _copyValuesScan
  */
 static ValuesScan *
@@ -1139,6 +1160,31 @@ _copyRangeVar(const RangeVar *from)
 }
 
 /*
+ * _copyTableFunc
+ */
+static TableFunc *
+_copyTableFunc(const TableFunc *from)
+{
+	TableFunc  *newnode = makeNode(TableFunc);
+
+	COPY_NODE_FIELD(ns_names);
+	COPY_NODE_FIELD(ns_uris);
+	COPY_NODE_FIELD(docexpr);
+	COPY_NODE_FIELD(rowexpr);
+	COPY_NODE_FIELD(colnames);
+	COPY_NODE_FIELD(coltypes);
+	COPY_NODE_FIELD(coltypmods);
+	COPY_NODE_FIELD(colcollations);
+	COPY_NODE_FIELD(colexprs);
+	COPY_NODE_FIELD(coldefexprs);
+	COPY_BITMAPSET_FIELD(notnulls);
+	COPY_SCALAR_FIELD(ordinalitycol);
+	COPY_LOCATION_FIELD(location);
+
+	return newnode;
+}
+
+/*
  * _copyIntoClause
  */
 static IntoClause *
@@ -2169,6 +2215,7 @@ _copyRangeTblEntry(const RangeTblEntry *from)
 	COPY_NODE_FIELD(joinaliasvars);
 	COPY_NODE_FIELD(functions);
 	COPY_SCALAR_FIELD(funcordinality);
+	COPY_NODE_FIELD(tablefunc);
 	COPY_NODE_FIELD(values_lists);
 	COPY_STRING_FIELD(ctename);
 	COPY_SCALAR_FIELD(ctelevelsup);
@@ -2590,6 +2637,38 @@ _copyRangeTableSample(const RangeTableSample *from)
 	return newnode;
 }
 
+static RangeTableFunc *
+_copyRangeTableFunc(const RangeTableFunc *from)
+{
+	RangeTableFunc *newnode = makeNode(RangeTableFunc);
+
+	COPY_SCALAR_FIELD(lateral);
+	COPY_NODE_FIELD(docexpr);
+	COPY_NODE_FIELD(rowexpr);
+	COPY_NODE_FIELD(namespaces);
+	COPY_NODE_FIELD(columns);
+	COPY_NODE_FIELD(alias);
+	COPY_LOCATION_FIELD(location);
+
+	return newnode;
+}
+
+static RangeTableFuncCol *
+_copyRangeTableFuncCol(const RangeTableFuncCol *from)
+{
+	RangeTableFuncCol *newnode = makeNode(RangeTableFuncCol);
+
+	COPY_STRING_FIELD(colname);
+	COPY_NODE_FIELD(typeName);
+	COPY_SCALAR_FIELD(for_ordinality);
+	COPY_SCALAR_FIELD(is_not_null);
+	COPY_NODE_FIELD(colexpr);
+	COPY_NODE_FIELD(coldefexpr);
+	COPY_LOCATION_FIELD(location);
+
+	return newnode;
+}
+
 static TypeCast *
 _copyTypeCast(const TypeCast *from)
 {
@@ -4540,6 +4619,9 @@ copyObject(const void *from)
 		case T_FunctionScan:
 			retval = _copyFunctionScan(from);
 			break;
+		case T_TableFuncScan:
+			retval = _copyTableFuncScan(from);
+			break;
 		case T_ValuesScan:
 			retval = _copyValuesScan(from);
 			break;
@@ -4616,6 +4698,9 @@ copyObject(const void *from)
 		case T_RangeVar:
 			retval = _copyRangeVar(from);
 			break;
+		case T_TableFunc:
+			retval = _copyTableFunc(from);
+			break;
 		case T_IntoClause:
 			retval = _copyIntoClause(from);
 			break;
@@ -5210,6 +5295,12 @@ copyObject(const void *from)
 		case T_RangeTableSample:
 			retval = _copyRangeTableSample(from);
 			break;
+		case T_RangeTableFunc:
+			retval = _copyRangeTableFunc(from);
+			break;
+		case T_RangeTableFuncCol:
+			retval = _copyRangeTableFuncCol(from);
+			break;
 		case T_TypeName:
 			retval = _copyTypeName(from);
 			break;