Implement table partitioning.

Table partitioning is like table inheritance and reuses much of the
existing infrastructure, but there are some important differences.
The parent is called a partitioned table and is always empty; it may
not have indexes or non-inherited constraints, since those make no
sense for a relation with no data of its own.  The children are called
partitions and contain all of the actual data.  Each partition has an
implicit partitioning constraint.  Multiple inheritance is not
allowed, and partitioning and inheritance can't be mixed.  Partitions
can't have extra columns and may not allow nulls unless the parent
does.  Tuples inserted into the parent are automatically routed to the
correct partition, so tuple-routing ON INSERT triggers are not needed.
Tuple routing isn't yet supported for partitions which are foreign
tables, and it doesn't handle updates that cross partition boundaries.

Currently, tables can be range-partitioned or list-partitioned.  List
partitioning is limited to a single column, but range partitioning can
involve multiple columns.  A partitioning "column" can be an
expression.

Because table partitioning is less general than table inheritance, it
is hoped that it will be easier to reason about properties of
partitions, and therefore that this will serve as a better foundation
for a variety of possible optimizations, including query planner
optimizations.  The tuple routing based which this patch does based on
the implicit partitioning constraints is an example of this, but it
seems likely that many other useful optimizations are also possible.

Amit Langote, reviewed and tested by Robert Haas, Ashutosh Bapat,
Amit Kapila, Rajkumar Raghuwanshi, Corey Huinker, Jaime Casanova,
Rushabh Lathia, Erik Rijkers, among others.  Minor revisions by me.

src/include/nodes/parsenodes.h

@@ -699,6 +699,79 @@ typedef struct XmlSerialize
 	int			location;		/* token location, or -1 if unknown */
 } XmlSerialize;
 
+/* Partitioning related definitions */
+
+/*
+ * PartitionElem - a column in the partition key
+ */
+typedef struct PartitionElem
+{
+	NodeTag		type;
+	char	   *name;		/* name of column to partition on, or NULL */
+	Node	   *expr;		/* expression to partition on, or NULL */
+	List	   *collation;	/* name of collation; NIL = default */
+	List	   *opclass;	/* name of desired opclass; NIL = default */
+	int			location;	/* token location, or -1 if unknown */
+} PartitionElem;
+
+/*
+ * PartitionSpec - partition key specification
+ */
+typedef struct PartitionSpec
+{
+	NodeTag		type;
+	char	   *strategy;	/* partitioning strategy ('list' or 'range') */
+	List	   *partParams; /* List of PartitionElems */
+	int			location;	/* token location, or -1 if unknown */
+} PartitionSpec;
+
+#define PARTITION_STRATEGY_LIST		'l'
+#define PARTITION_STRATEGY_RANGE	'r'
+
+/*
+ * PartitionBoundSpec - a partition bound specification
+ */
+typedef struct PartitionBoundSpec
+{
+	NodeTag		type;
+
+	char		strategy;
+
+	/* List partition values */
+	List	   *listdatums;
+
+	/*
+	 * Range partition lower and upper bounds; each member of the lists
+	 * is a PartitionRangeDatum (see below).
+	 */
+	List	   *lowerdatums;
+	List	   *upperdatums;
+
+	int			location;
+} PartitionBoundSpec;
+
+/*
+ * PartitionRangeDatum
+ */
+typedef struct PartitionRangeDatum
+{
+	NodeTag		type;
+
+	bool		infinite;
+	Node	   *value;
+
+	int			location;
+} PartitionRangeDatum;
+
+/*
+ * PartitionCmd -  ALTER TABLE partition commands
+ */
+typedef struct PartitionCmd
+{
+	NodeTag		type;
+	RangeVar   *name;
+	Node	   *bound;
+} PartitionCmd;
 
 /****************************************************************************
  *	Nodes for a Query tree
@@ -1549,7 +1622,9 @@ typedef enum AlterTableType
 	AT_DisableRowSecurity,		/* DISABLE ROW SECURITY */
 	AT_ForceRowSecurity,		/* FORCE ROW SECURITY */
 	AT_NoForceRowSecurity,		/* NO FORCE ROW SECURITY */
-	AT_GenericOptions			/* OPTIONS (...) */
+	AT_GenericOptions,			/* OPTIONS (...) */
+	AT_AttachPartition,			/* ATTACH PARTITION */
+	AT_DetachPartition			/* DETACH PARTITION */
 } AlterTableType;
 
 typedef struct ReplicaIdentityStmt
@@ -1775,6 +1850,8 @@ typedef struct CreateStmt
 	List	   *tableElts;		/* column definitions (list of ColumnDef) */
 	List	   *inhRelations;	/* relations to inherit from (list of
 								 * inhRelation) */
+	Node	   *partbound;		/* FOR VALUES clause */
+	PartitionSpec *partspec;	/* PARTITION BY clause */
 	TypeName   *ofTypename;		/* OF typename */
 	List	   *constraints;	/* constraints (list of Constraint nodes) */
 	List	   *options;		/* options from WITH clause */