Generated columns

This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.

This implements one kind of generated column: stored (computed on
write).  Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com

src/include/access/tupdesc.h

@@ -42,6 +42,7 @@ typedef struct TupleConstr
 	uint16		num_defval;
 	uint16		num_check;
 	bool		has_not_null;
+	bool		has_generated_stored;
 } TupleConstr;
 
 /*

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201903291
+#define CATALOG_VERSION_NO	201903301
 
 #endif

src/include/catalog/heap.h

@@ -28,6 +28,7 @@ typedef struct RawColumnDefault
 	AttrNumber	attnum;			/* attribute to attach default to */
 	Node	   *raw_default;	/* default value (untransformed parse tree) */
 	bool		missingMode;	/* true if part of add column processing */
+	char		generated;		/* attgenerated setting */
 } RawColumnDefault;
 
 typedef struct CookedConstraint
@@ -120,7 +121,8 @@ extern Node *cookDefault(ParseState *pstate,
 			Node *raw_default,
 			Oid atttypid,
 			int32 atttypmod,
-			const char *attname);
+			const char *attname,
+			char attgenerated);
 
 extern void DeleteRelationTuple(Oid relid);
 extern void DeleteAttributeTuples(Oid relid);

src/include/catalog/pg_attribute.h

@@ -140,6 +140,9 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	/* One of the ATTRIBUTE_IDENTITY_* constants below, or '\0' */
 	char		attidentity BKI_DEFAULT('\0');
 
+	/* One of the ATTRIBUTE_GENERATED_* constants below, or '\0' */
+	char		attgenerated BKI_DEFAULT('\0');
+
 	/* Is dropped (ie, logically invisible) or not */
 	bool		attisdropped BKI_DEFAULT(f);
 
@@ -201,6 +204,8 @@ typedef FormData_pg_attribute *Form_pg_attribute;
 #define		  ATTRIBUTE_IDENTITY_ALWAYS		'a'
 #define		  ATTRIBUTE_IDENTITY_BY_DEFAULT 'd'
 
+#define		  ATTRIBUTE_GENERATED_STORED	's'
+
 #endif							/* EXPOSE_TO_CLIENT_CODE */
 
 #endif							/* PG_ATTRIBUTE_H */

src/include/catalog/pg_class.dat

@@ -34,7 +34,7 @@
   relname => 'pg_attribute', reltype => 'pg_attribute', relam => 'heap',
   relfilenode => '0', relpages => '0', reltuples => '0', relallvisible => '0',
   reltoastrelid => '0', relhasindex => 'f', relisshared => 'f',
-  relpersistence => 'p', relkind => 'r', relnatts => '24', relchecks => '0',
+  relpersistence => 'p', relkind => 'r', relnatts => '25', relchecks => '0',
   relhasrules => 'f', relhastriggers => 'f', relhassubclass => 'f',
   relrowsecurity => 'f', relforcerowsecurity => 'f', relispopulated => 't',
   relreplident => 'n', relispartition => 'f', relfrozenxid => '3',

src/include/executor/nodeModifyTable.h

@@ -15,6 +15,8 @@
 
 #include "nodes/execnodes.h"
 
+extern void ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot);
+
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);

src/include/nodes/execnodes.h

@@ -452,6 +452,9 @@ typedef struct ResultRelInfo
 	/* array of constraint-checking expr states */
 	ExprState **ri_ConstraintExprs;
 
+	/* array of stored generated columns expr states */
+	ExprState **ri_GeneratedExprs;
+
 	/* for removing junk attributes from tuples */
 	JunkFilter *ri_junkFilter;
 

src/include/nodes/parsenodes.h

@@ -655,6 +655,7 @@ typedef struct ColumnDef
 	char		identity;		/* attidentity setting */
 	RangeVar   *identitySequence;	/* to store identity sequence name for
 									 * ALTER TABLE ... ADD COLUMN */
+	char		generated;		/* attgenerated setting */
 	CollateClause *collClause;	/* untransformed COLLATE spec, if any */
 	Oid			collOid;		/* collation OID (InvalidOid if not set) */
 	List	   *constraints;	/* other constraints on column */
@@ -677,10 +678,11 @@ typedef enum TableLikeOption
 	CREATE_TABLE_LIKE_COMMENTS = 1 << 0,
 	CREATE_TABLE_LIKE_CONSTRAINTS = 1 << 1,
 	CREATE_TABLE_LIKE_DEFAULTS = 1 << 2,
-	CREATE_TABLE_LIKE_IDENTITY = 1 << 3,
-	CREATE_TABLE_LIKE_INDEXES = 1 << 4,
-	CREATE_TABLE_LIKE_STATISTICS = 1 << 5,
-	CREATE_TABLE_LIKE_STORAGE = 1 << 6,
+	CREATE_TABLE_LIKE_GENERATED = 1 << 3,
+	CREATE_TABLE_LIKE_IDENTITY = 1 << 4,
+	CREATE_TABLE_LIKE_INDEXES = 1 << 5,
+	CREATE_TABLE_LIKE_STATISTICS = 1 << 6,
+	CREATE_TABLE_LIKE_STORAGE = 1 << 7,
 	CREATE_TABLE_LIKE_ALL = PG_INT32_MAX
 } TableLikeOption;
 
@@ -933,6 +935,15 @@ typedef struct PartitionCmd
  *	  them in these fields.  A whole-row Var reference is represented by
  *	  setting the bit for InvalidAttrNumber.
  *
+ *	  updatedCols is also used in some other places, for example, to determine
+ *	  which triggers to fire and in FDWs to know which changed columns they
+ *	  need to ship off.  Generated columns that are caused to be updated by an
+ *	  update to a base column are collected in extraUpdatedCols.  This is not
+ *	  considered for permission checking, but it is useful in those places
+ *	  that want to know the full set of columns being updated as opposed to
+ *	  only the ones the user explicitly mentioned in the query.  (There is
+ *	  currently no need for an extraInsertedCols, but it could exist.)
+ *
  *	  securityQuals is a list of security barrier quals (boolean expressions),
  *	  to be tested in the listed order before returning a row from the
  *	  relation.  It is always NIL in parser output.  Entries are added by the
@@ -1087,6 +1098,7 @@ typedef struct RangeTblEntry
 	Bitmapset  *selectedCols;	/* columns needing SELECT permission */
 	Bitmapset  *insertedCols;	/* columns needing INSERT permission */
 	Bitmapset  *updatedCols;	/* columns needing UPDATE permission */
+	Bitmapset  *extraUpdatedCols;	/* generated columns being updated */
 	List	   *securityQuals;	/* security barrier quals to apply, if any */
 } RangeTblEntry;
 
@@ -2086,6 +2098,7 @@ typedef enum ConstrType			/* types of constraints */
 	CONSTR_NOTNULL,
 	CONSTR_DEFAULT,
 	CONSTR_IDENTITY,
+	CONSTR_GENERATED,
 	CONSTR_CHECK,
 	CONSTR_PRIMARY,
 	CONSTR_UNIQUE,
@@ -2124,7 +2137,8 @@ typedef struct Constraint
 	bool		is_no_inherit;	/* is constraint non-inheritable? */
 	Node	   *raw_expr;		/* expr, as untransformed parse tree */
 	char	   *cooked_expr;	/* expr, as nodeToString representation */
-	char		generated_when;
+	char		generated_when;	/* ALWAYS or BY DEFAULT */
+	char		generated_kind; /* currently always STORED */
 
 	/* Fields used for unique constraints (UNIQUE and PRIMARY KEY): */
 	List	   *keys;			/* String nodes naming referenced key

src/include/optimizer/plancat.h

@@ -71,4 +71,6 @@ extern double get_function_rows(PlannerInfo *root, Oid funcid, Node *node);
 
 extern bool has_row_triggers(PlannerInfo *root, Index rti, CmdType event);
 
+extern bool has_stored_generated_columns(PlannerInfo *root, Index rti);
+
 #endif							/* PLANCAT_H */

src/include/parser/kwlist.h

@@ -383,6 +383,7 @@ PG_KEYWORD("statistics", STATISTICS, UNRESERVED_KEYWORD)
 PG_KEYWORD("stdin", STDIN, UNRESERVED_KEYWORD)
 PG_KEYWORD("stdout", STDOUT, UNRESERVED_KEYWORD)
 PG_KEYWORD("storage", STORAGE, UNRESERVED_KEYWORD)
+PG_KEYWORD("stored", STORED, UNRESERVED_KEYWORD)
 PG_KEYWORD("strict", STRICT_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("strip", STRIP_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("subscription", SUBSCRIPTION, UNRESERVED_KEYWORD)

src/include/parser/parse_node.h

@@ -71,7 +71,8 @@ typedef enum ParseExprKind
 	EXPR_KIND_PARTITION_BOUND,	/* partition bound expression */
 	EXPR_KIND_PARTITION_EXPRESSION, /* PARTITION BY expression */
 	EXPR_KIND_CALL_ARGUMENT,		/* procedure argument in CALL */
-	EXPR_KIND_COPY_WHERE		/* WHERE condition in COPY FROM */
+	EXPR_KIND_COPY_WHERE,		/* WHERE condition in COPY FROM */
+	EXPR_KIND_GENERATED_COLUMN,	/* generation expression for a column */
 } ParseExprKind;
 
 

src/include/utils/lsyscache.h

@@ -86,6 +86,7 @@ extern Oid get_opfamily_proc(Oid opfamily, Oid lefttype, Oid righttype,
 				  int16 procnum);
 extern char *get_attname(Oid relid, AttrNumber attnum, bool missing_ok);
 extern AttrNumber get_attnum(Oid relid, const char *attname);
+extern char get_attgenerated(Oid relid, AttrNumber attnum);
 extern Oid	get_atttype(Oid relid, AttrNumber attnum);
 extern void get_atttypetypmodcoll(Oid relid, AttrNumber attnum,
 					  Oid *typid, int32 *typmod, Oid *collid);