TABLESAMPLE, SQL Standard and extensible

Add a TABLESAMPLE clause to SELECT statements that allows
user to specify random BERNOULLI sampling or block level
SYSTEM sampling. Implementation allows for extensible
sampling functions to be written, using a standard API.
Basic version follows SQLStandard exactly. Usable
concrete use cases for the sampling API follow in later
commits.

Petr Jelinek

Reviewed by Michael Paquier and Simon Riggs

1 files changed, 60 insertions, 0 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 25839eed945..bdc7e61935c 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -642,6 +642,22 @@ _copyCustomScan(const CustomScan *from)
 }
 
 /*
+ * _copySampleScan
+ */
+static SampleScan *
+_copySampleScan(const SampleScan *from)
+{
+	SampleScan *newnode = makeNode(SampleScan);
+
+	/*
+	 * copy node superclass fields
+	 */
+	CopyScanFields((const Scan *) from, (Scan *) newnode);
+
+	return newnode;
+}
+
+/*
  * CopyJoinFields
  *
  *		This function copies the fields of the Join node.  It is used by
@@ -2063,6 +2079,7 @@ _copyRangeTblEntry(const RangeTblEntry *from)
 	COPY_SCALAR_FIELD(rtekind);
 	COPY_SCALAR_FIELD(relid);
 	COPY_SCALAR_FIELD(relkind);
+	COPY_NODE_FIELD(tablesample);
 	COPY_NODE_FIELD(subquery);
 	COPY_SCALAR_FIELD(security_barrier);
 	COPY_SCALAR_FIELD(jointype);
@@ -2224,6 +2241,40 @@ _copyCommonTableExpr(const CommonTableExpr *from)
 	return newnode;
 }
 
+static RangeTableSample *
+_copyRangeTableSample(const RangeTableSample *from)
+{
+	RangeTableSample *newnode = makeNode(RangeTableSample);
+
+	COPY_NODE_FIELD(relation);
+	COPY_STRING_FIELD(method);
+	COPY_NODE_FIELD(repeatable);
+	COPY_NODE_FIELD(args);
+
+	return newnode;
+}
+
+static TableSampleClause *
+_copyTableSampleClause(const TableSampleClause *from)
+{
+	TableSampleClause *newnode = makeNode(TableSampleClause);
+
+	COPY_SCALAR_FIELD(tsmid);
+	COPY_SCALAR_FIELD(tsmseqscan);
+	COPY_SCALAR_FIELD(tsmpagemode);
+	COPY_SCALAR_FIELD(tsminit);
+	COPY_SCALAR_FIELD(tsmnextblock);
+	COPY_SCALAR_FIELD(tsmnexttuple);
+	COPY_SCALAR_FIELD(tsmexaminetuple);
+	COPY_SCALAR_FIELD(tsmend);
+	COPY_SCALAR_FIELD(tsmreset);
+	COPY_SCALAR_FIELD(tsmcost);
+	COPY_NODE_FIELD(repeatable);
+	COPY_NODE_FIELD(args);
+
+	return newnode;
+}
+
 static A_Expr *
 _copyAExpr(const A_Expr *from)
 {
@@ -4179,6 +4230,9 @@ copyObject(const void *from)
 		case T_CustomScan:
 			retval = _copyCustomScan(from);
 			break;
+		case T_SampleScan:
+			retval = _copySampleScan(from);
+			break;
 		case T_Join:
 			retval = _copyJoin(from);
 			break;
@@ -4842,6 +4896,12 @@ copyObject(const void *from)
 		case T_CommonTableExpr:
 			retval = _copyCommonTableExpr(from);
 			break;
+		case T_RangeTableSample:
+			retval = _copyRangeTableSample(from);
+			break;
+		case T_TableSampleClause:
+			retval = _copyTableSampleClause(from);
+			break;
 		case T_FuncWithArgs:
 			retval = _copyFuncWithArgs(from);
 			break;