Apply 0001-on_update_set_default.patch

Author: hackorum

src/backend/access/common/reloptions.c

@@ -162,6 +162,15 @@ static relopt_bool boolRelOpts[] =
 		},
 		true
 	},
+	{
+		{
+			"on_update_set_default",
+			"Automatically set the column to its default value if the column has a default value in an UPDATE statement",
+			RELOPT_KIND_ATTRIBUTE,
+			ShareUpdateExclusiveLock
+		},
+		false
+	},
 	/* list terminator */
 	{{NULL}}
 };
@@ -2215,7 +2224,8 @@ attribute_reloptions(Datum reloptions, bool validate)
 {
 	static const relopt_parse_elt tab[] = {
 		{"n_distinct", RELOPT_TYPE_REAL, offsetof(AttributeOpts, n_distinct)},
-		{"n_distinct_inherited", RELOPT_TYPE_REAL, offsetof(AttributeOpts, n_distinct_inherited)}
+		{"n_distinct_inherited", RELOPT_TYPE_REAL, offsetof(AttributeOpts, n_distinct_inherited)},
+		{"on_update_set_default", RELOPT_TYPE_BOOL, offsetof(AttributeOpts, on_update_set_default)}
 	};
 
 	return (bytea *) build_reloptions(reloptions, validate,

src/backend/rewrite/rewriteHandler.c

@@ -42,6 +42,7 @@
 #include "rewrite/rewriteSearchCycle.h"
 #include "rewrite/rowsecurity.h"
 #include "tcop/tcopprot.h"
+#include "utils/attoptcache.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/rel.h"
@@ -899,6 +900,7 @@ rewriteTargetListIU(List *targetList,
 	{
 		TargetEntry *new_tle = new_tles[attrno - 1];
 		bool		apply_default;
+		bool		on_update_set_default = false;
 
 		att_tup = TupleDescAttr(target_relation->rd_att, attrno - 1);
 
@@ -1035,6 +1037,17 @@ rewriteTargetListIU(List *targetList,
 								NameStr(att_tup->attname)),
 						 errdetail("Column \"%s\" is a generated column.",
 								   NameStr(att_tup->attname))));
+
+			if (!new_tle)
+			{
+				AttributeOpts *aopt;
+
+				Assert(!apply_default);
+
+				aopt = get_attribute_options(target_relation->rd_id, attrno);
+				if (aopt != NULL && aopt->on_update_set_default)
+					on_update_set_default = true;
+			}
 		}
 
 		if (att_tup->attgenerated)
@@ -1076,6 +1089,24 @@ rewriteTargetListIU(List *targetList,
 										  pstrdup(NameStr(att_tup->attname)),
 										  false);
 		}
+		else if(on_update_set_default)
+		{
+			Node	*new_expr;
+
+			Assert(!new_tle);
+
+			new_expr = build_column_default(target_relation, attrno);
+			/*
+			 * If there is a default value, it should be automatically updated
+			 * to the default value; otherwise, we should not modify the value
+			 * of that column.
+			 */
+			if (new_expr)
+				new_tle = makeTargetEntry((Expr *) new_expr,
+										  attrno,
+										  pstrdup(NameStr(att_tup->attname)),
+										  false);
+		}
 
 		if (new_tle)
 			new_tlist = lappend(new_tlist, new_tle);

src/include/utils/attoptcache.h

@@ -21,6 +21,7 @@ typedef struct AttributeOpts
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
 	float8		n_distinct;
 	float8		n_distinct_inherited;
+	bool		on_update_set_default;
 } AttributeOpts;
 
 extern AttributeOpts *get_attribute_options(Oid attrelid, int attnum);