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

1 files changed, 27 insertions, 0 deletions

diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index d6cdd166073..400558b552b 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -2287,6 +2287,7 @@ transformUpdateTargetList(ParseState *pstate, List *origTlist)
 	RangeTblEntry *target_rte;
 	ListCell   *orig_tl;
 	ListCell   *tl;
+	TupleDesc	tupdesc = pstate->p_target_relation->rd_att;
 
 	tlist = transformTargetList(pstate, origTlist,
 								EXPR_KIND_UPDATE_SOURCE);
@@ -2345,6 +2346,32 @@ transformUpdateTargetList(ParseState *pstate, List *origTlist)
 	if (orig_tl != NULL)
 		elog(ERROR, "UPDATE target count mismatch --- internal error");
 
+	/*
+	 * Record in extraUpdatedCols generated columns referencing updated base
+	 * columns.
+	 */
+	if (tupdesc->constr &&
+		tupdesc->constr->has_generated_stored)
+	{
+		for (int i = 0; i < tupdesc->constr->num_defval; i++)
+		{
+			AttrDefault defval = tupdesc->constr->defval[i];
+			Node	   *expr;
+			Bitmapset  *attrs_used = NULL;
+
+			/* skip if not generated column */
+			if (!TupleDescAttr(tupdesc, defval.adnum - 1)->attgenerated)
+				continue;
+
+			expr = stringToNode(defval.adbin);
+			pull_varattnos(expr, 1, &attrs_used);
+
+			if (bms_overlap(target_rte->updatedCols, attrs_used))
+				target_rte->extraUpdatedCols = bms_add_member(target_rte->extraUpdatedCols,
+															  defval.adnum - FirstLowInvalidHeapAttributeNumber);
+		}
+	}
+
 	return tlist;
 }