Revert MERGE patch

This reverts commits d204ef63776b8a00ca220adec23979091564e465,
83454e3c2b28141c0db01c7d2027e01040df5249 and a few more commits thereafter
(complete list at the end) related to MERGE feature.

While the feature was fully functional, with sufficient test coverage and
necessary documentation, it was felt that some parts of the executor and
parse-analyzer can use a different design and it wasn't possible to do that in
the available time. So it was decided to revert the patch for PG11 and retry
again in the future.

Thanks again to all reviewers and bug reporters.

List of commits reverted, in reverse chronological order:

 f1464c5380 Improve parse representation for MERGE
 ddb4158579 MERGE syntax diagram correction
 530e69e59b Allow cpluspluscheck to pass by renaming variable
 01b88b4df5 MERGE minor errata
 3af7b2b0d4 MERGE fix variable warning in non-assert builds
 a5d86181ec MERGE INSERT allows only one VALUES clause
 4b2d44031f MERGE post-commit review
 4923550c20 Tab completion for MERGE
 aa3faa3c7a WITH support in MERGE
 83454e3c2b New files for MERGE
 d204ef6377 MERGE SQL Command following SQL:2016

Author: Pavan Deolasee
Reviewed-by: Michael Paquier

19 files changed, 20 insertions, 246 deletions

diff --git a/src/include/access/heapam.h b/src/include/access/heapam.h
index 7d756f20b0..ca5cad7497 100644
--- a/src/include/access/heapam.h
+++ b/src/include/access/heapam.h
@@ -53,34 +53,23 @@ typedef enum LockTupleMode
  * When heap_update, heap_delete, or heap_lock_tuple fail because the target
  * tuple is already outdated, they fill in this struct to provide information
  * to the caller about what happened.
- *
- * result is the result of HeapTupleSatisfiesUpdate, leading to the failure.
- * It's set to HeapTupleMayBeUpdated when there is no failure.
- *
  * ctid is the target's ctid link: it is the same as the target's TID if the
  * target was deleted, or the location of the replacement tuple if the target
  * was updated.
- *
  * xmax is the outdating transaction's XID.  If the caller wants to visit the
  * replacement tuple, it must check that this matches before believing the
  * replacement is really a match.
- *
  * cmax is the outdating command's CID, but only when the failure code is
  * HeapTupleSelfUpdated (i.e., something in the current transaction outdated
  * the tuple); otherwise cmax is zero.  (We make this restriction because
  * HeapTupleHeaderGetCmax doesn't work for tuples outdated in other
  * transactions.)
- *
- * lockmode is only relevant for callers of heap_update() and is the mode which
- * the caller should use in case it needs to lock the updated tuple.
  */
 typedef struct HeapUpdateFailureData
 {
-	HTSU_Result result;
 	ItemPointerData ctid;
 	TransactionId xmax;
 	CommandId	cmax;
-	LockTupleMode	lockmode;
 } HeapUpdateFailureData;
 
 
@@ -173,7 +162,7 @@ extern void heap_abort_speculative(Relation relation, HeapTuple tuple);
 extern HTSU_Result heap_update(Relation relation, ItemPointer otid,
 			HeapTuple newtup,
 			CommandId cid, Snapshot crosscheck, bool wait,
-			HeapUpdateFailureData *hufd);
+			HeapUpdateFailureData *hufd, LockTupleMode *lockmode);
 extern HTSU_Result heap_lock_tuple(Relation relation, HeapTuple tuple,
 				CommandId cid, LockTupleMode mode, LockWaitPolicy wait_policy,
 				bool follow_update,
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index 1b79a80310..a5b8610fa2 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -206,8 +206,7 @@ extern bool ExecBRDeleteTriggers(EState *estate,
 					 EPQState *epqstate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
-					 HeapTuple fdw_trigtuple,
-					 HeapUpdateFailureData *hufdp);
+					 HeapTuple fdw_trigtuple);
 extern void ExecARDeleteTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
@@ -226,8 +225,7 @@ extern TupleTableSlot *ExecBRUpdateTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
 					 HeapTuple fdw_trigtuple,
-					 TupleTableSlot *slot,
-					 HeapUpdateFailureData *hufdp);
+					 TupleTableSlot *slot);
 extern void ExecARUpdateTriggers(EState *estate,
 					 ResultRelInfo *relinfo,
 					 ItemPointer tupleid,
diff --git a/src/include/executor/execMerge.h b/src/include/executor/execMerge.h
deleted file mode 100644
index 5ea8c4e50a..0000000000
--- a/src/include/executor/execMerge.h
+++ /dev/null
@@ -1,31 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * execMerge.h
- *
- *
- * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * src/include/executor/execMerge.h
- *
- *-------------------------------------------------------------------------
- */
-#ifndef EXECMERGE_H
-#define EXECMERGE_H
-
-#include "nodes/execnodes.h"
-
-/* flags for mt_merge_subcommands */
-#define MERGE_INSERT	0x01
-#define MERGE_UPDATE	0x02
-#define MERGE_DELETE	0x04
-
-extern void ExecMerge(ModifyTableState *mtstate, EState *estate,
-					  TupleTableSlot *slot, JunkFilter *junkfilter,
-					  ResultRelInfo *resultRelInfo);
-
-extern void ExecInitMerge(ModifyTableState *mtstate,
-						  EState *estate,
-						  ResultRelInfo *resultRelInfo);
-
-#endif							/* NODEMERGE_H */
diff --git a/src/include/executor/execPartition.h b/src/include/executor/execPartition.h
index b2daf24c41..0c36c8be30 100644
--- a/src/include/executor/execPartition.h
+++ b/src/include/executor/execPartition.h
@@ -186,7 +186,6 @@ extern int ExecFindPartition(ResultRelInfo *resultRelInfo,
 				  PartitionDispatch *pd,
 				  TupleTableSlot *slot,
 				  EState *estate);
-extern int ExecFindPartitionByOid(PartitionTupleRouting *proute, Oid partoid);
 extern ResultRelInfo *ExecInitPartitionInfo(ModifyTableState *mtstate,
 					ResultRelInfo *resultRelInfo,
 					PartitionTupleRouting *proute,
diff --git a/src/include/executor/instrument.h b/src/include/executor/instrument.h
index 1bc7a88dbd..6e3c71759b 100644
--- a/src/include/executor/instrument.h
+++ b/src/include/executor/instrument.h
@@ -59,11 +59,8 @@ typedef struct Instrumentation
 	double		ntuples;		/* Total tuples produced */
 	double		ntuples2;		/* Secondary node-specific tuple counter */
 	double		nloops;			/* # of run cycles for this node */
-	double		nfiltered1;		/* # tuples removed by scanqual or joinqual OR
-								 * # tuples inserted by MERGE */
-	double		nfiltered2;		/* # tuples removed by "other" quals OR
-								 * # tuples updated by MERGE */
-	double		nfiltered3;		/* # tuples deleted by MERGE */
+	double      nfiltered1;     /* # tuples removed by scanqual or joinqual */
+	double      nfiltered2;     /* # tuples removed by "other" quals */
 	BufferUsage bufusage;		/* Total buffer usage */
 } Instrumentation;
 
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 7e9ab3cb6b..0d7e579e1c 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -18,28 +18,5 @@
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
-extern TupleTableSlot *ExecPrepareTupleRouting(ModifyTableState *mtstate,
-						EState *estate,
-						struct PartitionTupleRouting *proute,
-						ResultRelInfo *targetRelInfo,
-						TupleTableSlot *slot);
-extern TupleTableSlot *ExecDelete(ModifyTableState *mtstate,
-		   ItemPointer tupleid, HeapTuple oldtuple, TupleTableSlot *planSlot,
-		   EPQState *epqstate, EState *estate, bool *tupleDeleted,
-		   bool processReturning, HeapUpdateFailureData *hufdp,
-		   MergeActionState *actionState, bool canSetTag,
-		   bool changingPart);
-extern TupleTableSlot *ExecUpdate(ModifyTableState *mtstate,
-		   ItemPointer tupleid, HeapTuple oldtuple, TupleTableSlot *slot,
-		   TupleTableSlot *planSlot, EPQState *epqstate, EState *estate,
-		   bool *tuple_updated, HeapUpdateFailureData *hufdp,
-		   MergeActionState *actionState, bool canSetTag);
-extern TupleTableSlot *ExecInsert(ModifyTableState *mtstate,
-		   TupleTableSlot *slot,
-		   TupleTableSlot *planSlot,
-		   EState *estate,
-		   MergeActionState *actionState,
-		   bool canSetTag);
-extern void ExecCheckPlanOutput(Relation resultRel, List *targetList);
 
 #endif							/* NODEMODIFYTABLE_H */
diff --git a/src/include/executor/spi.h b/src/include/executor/spi.h
index 78410b9f77..e5bdaecc4e 100644
--- a/src/include/executor/spi.h
+++ b/src/include/executor/spi.h
@@ -64,7 +64,6 @@ typedef struct _SPI_plan *SPIPlanPtr;
 #define SPI_OK_REL_REGISTER		15
 #define SPI_OK_REL_UNREGISTER	16
 #define SPI_OK_TD_REGISTER		17
-#define SPI_OK_MERGE			18
 
 #define SPI_OPT_NONATOMIC		(1 << 0)
 
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index c53e113269..9fe0b79095 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -363,17 +363,8 @@ typedef struct JunkFilter
 	AttrNumber *jf_cleanMap;
 	TupleTableSlot *jf_resultSlot;
 	AttrNumber	jf_junkAttNo;
-	AttrNumber	jf_otherJunkAttNo;
 } JunkFilter;
 
-typedef struct MergeState
-{
-	/* List of MERGE MATCHED action states */
-	List		   *matchedActionStates;
-	/* List of MERGE NOT MATCHED action states */
-	List		   *notMatchedActionStates;
-} MergeState;
-
 /*
  * OnConflictSetState
  *
@@ -470,38 +461,8 @@ typedef struct ResultRelInfo
 
 	/* true if ready for tuple routing */
 	bool		ri_PartitionReadyForRouting;
-
-	int			ri_PartitionLeafIndex;
-	/* for running MERGE on this result relation */
-	MergeState *ri_mergeState;
-
-	/*
-	 * While executing MERGE, the target relation is processed twice; once
-	 * as a target relation and once to run a join between the target and the
-	 * source. We generate two different RTEs for these two purposes, one with
-	 * rte->inh set to false and other with rte->inh set to true.
-	 *
-	 * Since the plan re-evaluated by EvalPlanQual uses the join RTE, we must
-	 * install the updated tuple in the scan corresponding to that RTE. The
-	 * following member tracks the index of the second RTE for EvalPlanQual
-	 * purposes. ri_mergeTargetRTI is non-zero only when MERGE is in-progress.
-	 * We use ri_mergeTargetRTI to run EvalPlanQual for MERGE and
-	 * ri_RangeTableIndex elsewhere.
-	 */
-	Index		ri_mergeTargetRTI;
 } ResultRelInfo;
 
-/*
- * Get the Range table index for EvalPlanQual.
- *
- * We use the ri_mergeTargetRTI if set, otherwise use ri_RangeTableIndex.
- * ri_mergeTargetRTI should really be ever set iff we're running MERGE.
- */
-#define GetEPQRangeTableIndex(r) \
-	(((r)->ri_mergeTargetRTI > 0)  \
-	 ? (r)->ri_mergeTargetRTI \
-	 : (r)->ri_RangeTableIndex)
-
 /* ----------------
  *	  EState information
  *
@@ -1019,11 +980,6 @@ typedef struct PlanState
 		if (((PlanState *)(node))->instrument) \
 			((PlanState *)(node))->instrument->nfiltered2 += (delta); \
 	} while(0)
-#define InstrCountFiltered3(node, delta) \
-	do { \
-		if (((PlanState *)(node))->instrument) \
-			((PlanState *)(node))->instrument->nfiltered3 += (delta); \
-	} while(0)
 
 /*
  * EPQState is state for executing an EvalPlanQual recheck on a candidate
@@ -1071,27 +1027,13 @@ typedef struct ProjectSetState
 } ProjectSetState;
 
 /* ----------------
- *	 MergeActionState information
- * ----------------
- */
-typedef struct MergeActionState
-{
-	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
-	ExprState  *whenqual;		/* WHEN AND conditions */
-	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
-	ProjectionInfo *proj;		/* tuple projection info */
-	TupleDesc	tupDesc;		/* tuple descriptor for projection */
-} MergeActionState;
-
-/* ----------------
  *	 ModifyTableState information
  * ----------------
  */
 typedef struct ModifyTableState
 {
 	PlanState	ps;				/* its first field is NodeTag */
-	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
+	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	bool		mt_done;		/* are we done? */
 	PlanState **mt_plans;		/* subplans (one per target rel) */
@@ -1107,8 +1049,6 @@ typedef struct ModifyTableState
 	List	   *mt_excludedtlist;	/* the excluded pseudo relation's tlist  */
 	TupleTableSlot *mt_conflproj;	/* CONFLICT ... SET ... projection target */
 
-	TupleTableSlot *mt_mergeproj;	/* MERGE action projection target */
-
 	/* Tuple-routing support info */
 	struct PartitionTupleRouting *mt_partition_tuple_routing;
 
@@ -1120,9 +1060,6 @@ typedef struct ModifyTableState
 
 	/* Per plan map for tuple conversion from child to root */
 	TupleConversionMap **mt_per_subplan_tupconv_maps;
-
-	/* Flags showing which subcommands are present INS/UPD/DEL/DO NOTHING */
-	int			mt_merge_subcommands;
 } ModifyTableState;
 
 /* ----------------
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index defdbae507..adb159a6da 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -97,7 +97,6 @@ typedef enum NodeTag
 	T_PlanState,
 	T_ResultState,
 	T_ProjectSetState,
-	T_MergeActionState,
 	T_ModifyTableState,
 	T_AppendState,
 	T_MergeAppendState,
@@ -272,7 +271,6 @@ typedef enum NodeTag
 	T_RollupData,
 	T_GroupingSetData,
 	T_StatisticExtInfo,
-	T_MergeAction,
 
 	/*
 	 * TAGS FOR MEMORY NODES (memnodes.h)
@@ -313,7 +311,6 @@ typedef enum NodeTag
 	T_InsertStmt,
 	T_DeleteStmt,
 	T_UpdateStmt,
-	T_MergeStmt,
 	T_SelectStmt,
 	T_AlterTableStmt,
 	T_AlterTableCmd,
@@ -478,7 +475,6 @@ typedef enum NodeTag
 	T_PartitionRangeDatum,
 	T_PartitionCmd,
 	T_VacuumRelation,
-	T_MergeWhenClause,
 
 	/*
 	 * TAGS FOR REPLICATION GRAMMAR PARSE NODES (replnodes.h)
@@ -664,8 +660,7 @@ typedef enum CmdType
 	CMD_SELECT,					/* select stmt */
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
-	CMD_DELETE,					/* delete stmt */
-	CMD_MERGE,					/* merge stmt */
+	CMD_DELETE,
 	CMD_UTILITY,				/* cmds like create, destroy, copy, vacuum,
 								 * etc. */
 	CMD_NOTHING					/* dummy command for instead nothing rules
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index c8405386cf..de020e68a4 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -38,7 +38,7 @@ typedef enum OverridingKind
 typedef enum QuerySource
 {
 	QSRC_ORIGINAL,				/* original parsetree (explicit query) */
-	QSRC_PARSER,				/* added by parse analysis in MERGE */
+	QSRC_PARSER,				/* added by parse analysis (now unused) */
 	QSRC_INSTEAD_RULE,			/* added by unconditional INSTEAD rule */
 	QSRC_QUAL_INSTEAD_RULE,		/* added by conditional INSTEAD rule */
 	QSRC_NON_INSTEAD_RULE		/* added by non-INSTEAD rule */
@@ -107,7 +107,7 @@ typedef struct Query
 {
 	NodeTag		type;
 
-	CmdType		commandType;	/* select|insert|update|delete|merge|utility */
+	CmdType		commandType;	/* select|insert|update|delete|utility */
 
 	QuerySource querySource;	/* where did I come from? */
 
@@ -118,7 +118,7 @@ typedef struct Query
 	Node	   *utilityStmt;	/* non-null if commandType == CMD_UTILITY */
 
 	int			resultRelation; /* rtable index of target relation for
-								 * INSERT/UPDATE/DELETE/MERGE; 0 for SELECT */
+								 * INSERT/UPDATE/DELETE; 0 for SELECT */
 
 	bool		hasAggs;		/* has aggregates in tlist or havingQual */
 	bool		hasWindowFuncs; /* has window functions in tlist */
@@ -169,9 +169,6 @@ typedef struct Query
 	List	   *withCheckOptions;	/* a list of WithCheckOption's, which are
 									 * only added during rewrite and therefore
 									 * are not written out as part of Query. */
-	int			mergeTarget_relation;
-	List	   *mergeSourceTargetList;
-	List	   *mergeActionList;	/* list of actions for MERGE (only) */
 
 	/*
 	 * The following two fields identify the portion of the source text string
@@ -1131,9 +1128,7 @@ typedef enum WCOKind
 	WCO_VIEW_CHECK,				/* WCO on an auto-updatable view */
 	WCO_RLS_INSERT_CHECK,		/* RLS INSERT WITH CHECK policy */
 	WCO_RLS_UPDATE_CHECK,		/* RLS UPDATE WITH CHECK policy */
-	WCO_RLS_CONFLICT_CHECK,		/* RLS ON CONFLICT DO UPDATE USING policy */
-	WCO_RLS_MERGE_UPDATE_CHECK, /* RLS MERGE UPDATE USING policy */
-	WCO_RLS_MERGE_DELETE_CHECK	/* RLS MERGE DELETE USING policy */
+	WCO_RLS_CONFLICT_CHECK		/* RLS ON CONFLICT DO UPDATE USING policy */
 } WCOKind;
 
 typedef struct WithCheckOption
@@ -1509,46 +1504,6 @@ typedef struct UpdateStmt
 } UpdateStmt;
 
 /* ----------------------
- *		Merge Statement
- * ----------------------
- */
-typedef struct MergeStmt
-{
-	NodeTag		type;
-	RangeVar   *relation;			/* target relation to merge into */
-	Node	   *source_relation;	/* source relation */
-	Node	   *join_condition; /* join condition between source and target */
-	List	   *mergeWhenClauses;	/* list of MergeWhenClause(es) */
-	WithClause *withClause;		/* WITH clause */
-} MergeStmt;
-
-typedef struct MergeWhenClause
-{
-	NodeTag		type;
-	bool		matched;		/* true=MATCHED, false=NOT MATCHED */
-	CmdType		commandType;	/* INSERT/UPDATE/DELETE/DO NOTHING */
-	Node	   *condition;		/* WHEN AND conditions (raw parser) */
-	List	   *targetList;		/* INSERT/UPDATE targetlist */
-	/* the following members are only useful for INSERT action */
-	List	   *cols;			/* optional: names of the target columns */
-	List	   *values;			/* VALUES to INSERT, or NULL */
-	OverridingKind override;	/* OVERRIDING clause */
-} MergeWhenClause;
-
-/*
- * WHEN [NOT] MATCHED THEN action info
- */
-typedef struct MergeAction
-{
-	NodeTag     type;
-	bool        matched;        /* true=MATCHED, false=NOT MATCHED */
-	OverridingKind	override;	/* OVERRIDING clause */
-	Node       *qual;           /* transformed WHEN AND conditions */
-	CmdType     commandType;    /* INSERT/UPDATE/DELETE/DO NOTHING */
-	List       *targetList;     /* the target list (of ResTarget) */
-} MergeAction;
-
-/* ----------------------
  *		Select Statement
  *
  * A "simple" SELECT is represented in the output of gram.y by a single
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index c5c33cd336..f2dda82e66 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -18,7 +18,6 @@
 #include "lib/stringinfo.h"
 #include "nodes/bitmapset.h"
 #include "nodes/lockoptions.h"
-#include "nodes/parsenodes.h"
 #include "nodes/primnodes.h"
 
 
@@ -43,7 +42,7 @@ typedef struct PlannedStmt
 {
 	NodeTag		type;
 
-	CmdType		commandType;	/* select|insert|update|delete|merge|utility */
+	CmdType		commandType;	/* select|insert|update|delete|utility */
 
 	uint64		queryId;		/* query identifier (copied from Query) */
 
@@ -217,14 +216,13 @@ typedef struct ProjectSet
 typedef struct ModifyTable
 {
 	Plan		plan;
-	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
+	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	Index		nominalRelation;	/* Parent RT index for use of EXPLAIN */
 	/* RT indexes of non-leaf tables in a partition tree */
 	List	   *partitioned_rels;
 	bool		partColsUpdated;	/* some part key in hierarchy updated */
 	List	   *resultRelations;	/* integer list of RT indexes */
-	Index	    mergeTargetRelation;	/* RT index of the merge target */
 	int			resultRelIndex; /* index of first resultRel in plan's list */
 	int			rootResultRelIndex; /* index of the partitioned table root */
 	List	   *plans;			/* plan(s) producing source data */
@@ -240,8 +238,6 @@ typedef struct ModifyTable
 	Node	   *onConflictWhere;	/* WHERE for ON CONFLICT UPDATE */
 	Index		exclRelRTI;		/* RTI of the EXCLUDED pseudo relation */
 	List	   *exclRelTlist;	/* tlist of the EXCLUDED pseudo relation */
-	List	   *mergeSourceTargetList;
-	List	   *mergeActionList;	/* actions for MERGE */
 } ModifyTable;
 
 /* ----------------
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 73a41c5475..d6dbf15a4b 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -1684,7 +1684,7 @@ typedef struct LockRowsPath
 } LockRowsPath;
 
 /*
- * ModifyTablePath represents performing INSERT/UPDATE/DELETE/MERGE
+ * ModifyTablePath represents performing INSERT/UPDATE/DELETE modifications
  *
  * We represent most things that will be in the ModifyTable plan node
  * literally, except we have child Path(s) not Plan(s).  But analysis of the
@@ -1693,14 +1693,13 @@ typedef struct LockRowsPath
 typedef struct ModifyTablePath
 {
 	Path		path;
-	CmdType		operation;		/* INSERT, UPDATE, DELETE or MERGE */
+	CmdType		operation;		/* INSERT, UPDATE, or DELETE */
 	bool		canSetTag;		/* do we set the command tag/es_processed? */
 	Index		nominalRelation;	/* Parent RT index for use of EXPLAIN */
 	/* RT indexes of non-leaf tables in a partition tree */
 	List	   *partitioned_rels;
 	bool		partColsUpdated;	/* some part key in hierarchy updated */
 	List	   *resultRelations;	/* integer list of RT indexes */
-	Index		mergeTargetRelation;	/* RT index of merge target relation */
 	List	   *subpaths;		/* Path(s) producing source data */
 	List	   *subroots;		/* per-target-table PlannerInfos */
 	List	   *withCheckOptionLists;	/* per-target-table WCO lists */
@@ -1708,8 +1707,6 @@ typedef struct ModifyTablePath
 	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
 	OnConflictExpr *onconflict; /* ON CONFLICT clause, or NULL */
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
-	List	   *mergeSourceTargetList;
-	List	   *mergeActionList;	/* actions for MERGE */
 } ModifyTablePath;
 
 /*
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 4f65686d9b..e99ae36bef 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -241,14 +241,11 @@ extern ModifyTablePath *create_modifytable_path(PlannerInfo *root,
 						CmdType operation, bool canSetTag,
 						Index nominalRelation, List *partitioned_rels,
 						bool partColsUpdated,
-						List *resultRelations,
-						Index	mergeTargetRelation,
-						List *subpaths,
+						List *resultRelations, List *subpaths,
 						List *subroots,
 						List *withCheckOptionLists, List *returningLists,
 						List *rowMarks, OnConflictExpr *onconflict,
-						List *mergeSourceTargetList,
-						List *mergeActionList, int epqParam);
+						int epqParam);
 extern LimitPath *create_limit_path(PlannerInfo *root, RelOptInfo *rel,
 				  Path *subpath,
 				  Node *limitOffset, Node *limitCount,
diff --git a/src/include/parser/analyze.h b/src/include/parser/analyze.h
index 41fb10666e..687ae1b5b7 100644
--- a/src/include/parser/analyze.h
+++ b/src/include/parser/analyze.h
@@ -32,11 +32,6 @@ extern Query *parse_sub_analyze(Node *parseTree, ParseState *parentParseState,
 				  bool locked_from_parent,
 				  bool resolve_unknowns);
 
-extern List *transformInsertRow(ParseState *pstate, List *exprlist,
-				   List *stmtcols, List *icolumns, List *attrnos,
-				   bool strip_indirection);
-extern List *transformUpdateTargetList(ParseState *pstate,
-						  List *targetList);
 extern Query *transformTopLevelStmt(ParseState *pstate, RawStmt *parseTree);
 extern Query *transformStmt(ParseState *pstate, Node *parseTree);
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 81f758afbf..23db40147b 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -245,10 +245,8 @@ PG_KEYWORD("locked", LOCKED, UNRESERVED_KEYWORD)
 PG_KEYWORD("logged", LOGGED, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
-PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("materialized", MATERIALIZED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
-PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("method", METHOD, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index 4420e72070..2c0e092862 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -20,10 +20,7 @@ extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
 extern bool interpretOidsOption(List *defList, bool allowOids);
-extern Node *transformFromClauseItem(ParseState *pstate, Node *n,
-						RangeTblEntry **top_rte, int *top_rti,
-						RangeTblEntry **right_rte, int *right_rti,
-						List **fnamespace);
+
 extern Node *transformWhereClause(ParseState *pstate, Node *clause,
 					 ParseExprKind exprKind, const char *constructName);
 extern Node *transformLimitClause(ParseState *pstate, Node *clause,
diff --git a/src/include/parser/parse_merge.h b/src/include/parser/parse_merge.h
deleted file mode 100644
index 0151809e09..0000000000
--- a/src/include/parser/parse_merge.h
+++ /dev/null
@@ -1,19 +0,0 @@
-/*-------------------------------------------------------------------------
- *
- * parse_merge.h
- *	  handle merge-stmt in parser
- *
- *
- * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
- * Portions Copyright (c) 1994, Regents of the University of California
- *
- * src/include/parser/parse_merge.h
- *
- *-------------------------------------------------------------------------
- */
-#ifndef PARSE_MERGE_H
-#define PARSE_MERGE_H
-
-#include "parser/parse_node.h"
-extern Query *transformMergeStmt(ParseState *pstate, MergeStmt *stmt);
-#endif
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 3fd2151ccb..0230543810 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -50,7 +50,6 @@ typedef enum ParseExprKind
 	EXPR_KIND_INSERT_TARGET,	/* INSERT target list item */
 	EXPR_KIND_UPDATE_SOURCE,	/* UPDATE assignment source item */
 	EXPR_KIND_UPDATE_TARGET,	/* UPDATE assignment target item */
-	EXPR_KIND_MERGE_WHEN_AND,	/* MERGE WHEN ... AND condition */
 	EXPR_KIND_GROUP_BY,			/* GROUP BY */
 	EXPR_KIND_ORDER_BY,			/* ORDER BY */
 	EXPR_KIND_DISTINCT_ON,		/* DISTINCT ON */
@@ -128,7 +127,7 @@ typedef Node *(*CoerceParamHook) (ParseState *pstate, Param *param,
  * p_parent_cte: CommonTableExpr that immediately contains the current query,
  * if any.
  *
- * p_target_relation: target relation, if query is INSERT/UPDATE/DELETE/MERGE
+ * p_target_relation: target relation, if query is INSERT, UPDATE, or DELETE.
  *
  * p_target_rangetblentry: target relation's entry in the rtable list.
  *
@@ -182,7 +181,7 @@ struct ParseState
 	List	   *p_ctenamespace; /* current namespace for common table exprs */
 	List	   *p_future_ctes;	/* common table exprs not yet in namespace */
 	CommonTableExpr *p_parent_cte;	/* this query's containing CTE */
-	Relation	p_target_relation;	/* INSERT/UPDATE/DELETE/MERGE target rel */
+	Relation	p_target_relation;	/* INSERT/UPDATE/DELETE target rel */
 	RangeTblEntry *p_target_rangetblentry;	/* target rel's RTE */
 	bool		p_is_insert;	/* process assignment like INSERT not UPDATE */
 	List	   *p_windowdefs;	/* raw representations of window clauses */
diff --git a/src/include/rewrite/rewriteHandler.h b/src/include/rewrite/rewriteHandler.h
index 1ab5de3942..8128199fc3 100644
--- a/src/include/rewrite/rewriteHandler.h
+++ b/src/include/rewrite/rewriteHandler.h
@@ -25,7 +25,6 @@ extern void AcquireRewriteLocks(Query *parsetree,
 extern Node *build_column_default(Relation rel, int attrno);
 extern void rewriteTargetListUD(Query *parsetree, RangeTblEntry *target_rte,
 					Relation target_relation);
-extern void rewriteTargetListMerge(Query *parsetree, Relation target_relation);
 
 extern Query *get_view_query(Relation view);
 extern const char *view_query_is_auto_updatable(Query *viewquery,