UPDATE ... SET <col> = DEFAULT

Rod Taylor

doc/src/sgml/ref/update.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/update.sgml,v 1.21 2003/04/26 23:56:51 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/update.sgml,v 1.22 2003/06/25 04:19:24 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -16,7 +16,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replaceable class="PARAMETER">column</replaceable> = <replaceable class="PARAMETER">expression</replaceable> [, ...]
+UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...]
     [ FROM <replaceable class="PARAMETER">fromlist</replaceable> ]
     [ WHERE <replaceable class="PARAMETER">condition</replaceable> ]
 </synopsis>
@@ -77,6 +77,15 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replacea
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>DEFAULT</literal></term>
+    <listitem>
+     <para>
+      This column will be filled with its default value.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="PARAMETER">fromlist</replaceable></term>
     <listitem>

src/backend/nodes/copyfuncs.c

@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.254 2003/06/25 03:40:17 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.255 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1661,10 +1661,10 @@ _copyFuncWithArgs(FuncWithArgs *from)
 	return newnode;
 }
 
-static InsertDefault *
-_copyInsertDefault(InsertDefault *from)
+static SetToDefault *
+_copySetToDefault(SetToDefault *from)
 {
-	InsertDefault *newnode = makeNode(InsertDefault);
+	SetToDefault *newnode = makeNode(SetToDefault);
 
 	return newnode;
 }
@@ -2942,8 +2942,8 @@ copyObject(void *from)
 		case T_FuncWithArgs:
 			retval = _copyFuncWithArgs(from);
 			break;
-		case T_InsertDefault:
-			retval = _copyInsertDefault(from);
+		case T_SetToDefault:
+			retval = _copySetToDefault(from);
 			break;
 
 		default:

src/backend/nodes/equalfuncs.c

@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/nodes/equalfuncs.c,v 1.197 2003/06/25 03:40:17 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/nodes/equalfuncs.c,v 1.198 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -728,7 +728,7 @@ _equalFuncWithArgs(FuncWithArgs *a, FuncWithArgs *b)
 }
 
 static bool
-_equalInsertDefault(InsertDefault *a, InsertDefault *b)
+_equalSetToDefault(SetToDefault *a, SetToDefault *b)
 {
 	return true;
 }
@@ -2055,8 +2055,8 @@ equal(void *a, void *b)
 		case T_FuncWithArgs:
 			retval = _equalFuncWithArgs(a, b);
 			break;
-		case T_InsertDefault:
-			retval = _equalInsertDefault(a, b);
+		case T_SetToDefault:
+			retval = _equalSetToDefault(a, b);
 			break;
 
 		default:

src/backend/parser/analyze.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.276 2003/06/25 03:40:17 momjian Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/parser/analyze.c,v 1.277 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -660,23 +660,9 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt,
 		col = (ResTarget *) lfirst(icolumns);
 		Assert(IsA(col, ResTarget));
 
-		/*
-		 * When the value is to be set to the column default we can simply
-		 * drop the TLE now and handle it later on using methods for missing
-		 * columns.
-		 */
-		if (IsA(tle, InsertDefault))
-		{
-			qry->targetList = lremove(tle, qry->targetList);
-			/* Note: the stmt->cols list is not adjusted to match */
-		}
-		else
-		{
-			/* Normal case */
-			Assert(!tle->resdom->resjunk);
-			updateTargetListEntry(pstate, tle, col->name, lfirsti(attnos),
-								  col->indirection);
-		}
+		Assert(!tle->resdom->resjunk);
+		updateTargetListEntry(pstate, tle, col->name, lfirsti(attnos),
+							  col->indirection);
 
 		icolumns = lnext(icolumns);
 		attnos = lnext(attnos);
@@ -2431,10 +2417,12 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 		if (origTargetList == NIL)
 			elog(ERROR, "UPDATE target count mismatch --- internal error");
 		origTarget = (ResTarget *) lfirst(origTargetList);
+
 		updateTargetListEntry(pstate, tle, origTarget->name,
 							  attnameAttNum(pstate->p_target_relation,
 											origTarget->name, true),
 							  origTarget->indirection);
+
 		origTargetList = lnext(origTargetList);
 	}
 	if (origTargetList != NIL)

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.419 2003/06/25 03:40:18 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.420 2003/06/25 04:19:24 momjian Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -6945,6 +6945,15 @@ update_target_el:
 					$$->indirection = $2;
 					$$->val = (Node *)$4;
 				}
+			| ColId opt_indirection '=' DEFAULT
+				{
+					SetToDefault *def = makeNode(SetToDefault);
+					$$ = makeNode(ResTarget);
+					$$->name = $1;
+					$$->indirection = NULL;
+					$$->val = (Node *)def;
+				}
+
 		;
 
 insert_target_list:
@@ -6956,7 +6965,7 @@ insert_target_el:
 			target_el								{ $$ = $1; }
 			| DEFAULT
 				{
-					InsertDefault *def = makeNode(InsertDefault);
+					SetToDefault *def = makeNode(SetToDefault);
 					$$ = makeNode(ResTarget);
 					$$->name = NULL;
 					$$->indirection = NULL;

src/backend/parser/parse_target.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_target.c,v 1.102 2003/05/31 19:03:34 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_target.c,v 1.103 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -177,19 +177,24 @@ transformTargetList(ParseState *pstate, List *targetlist)
 														false));
 			}
 		}
-		else if (IsA(res->val, InsertDefault))
+		else if (IsA(res->val, SetToDefault))
 		{
-			InsertDefault *newnode = makeNode(InsertDefault);
-
 			/*
-			 * If this is a DEFAULT element, we make a junk entry which
-			 * will get dropped on return to transformInsertStmt().
+			 * If this is a DEFAULT element, we make a standard entry using
+			 * the default for the target expression.  rewriteTargetList will
+			 * substitute the columns default for this expression.
 			 */
-			p_target = lappend(p_target, newnode);
+			p_target = lappend(p_target,
+							   makeTargetEntry(makeResdom((AttrNumber) pstate->p_next_resno++,
+														  UNKNOWNOID,
+														  -1,
+														  res->name,
+														  false),
+											   (Expr *) res->val));
 		}
 		else
 		{
-			/* Everything else but ColumnRef and InsertDefault */
+			/* Everything else but ColumnRef and SetToDefault */
 			p_target = lappend(p_target,
 							   transformTargetEntry(pstate,
 													res->val,
@@ -321,9 +326,10 @@ updateTargetListEntry(ParseState *pstate,
 					  int attrno,
 					  List *indirection)
 {
-	Oid			type_id = exprType((Node *) tle->expr);	/* type of value provided */
+	Oid			type_id; 		/* type of value provided */
 	Oid			attrtype;		/* type of target column */
 	int32		attrtypmod;
+	bool		isDefault = false;
 	Resdom	   *resnode = tle->resdom;
 	Relation	rd = pstate->p_target_relation;
 
@@ -333,6 +339,17 @@ updateTargetListEntry(ParseState *pstate,
 	attrtype = attnumTypeId(rd, attrno);
 	attrtypmod = rd->rd_att->attrs[attrno - 1]->atttypmod;
 
+	/* The type of the default column is equivalent to that of the column */
+	if (tle->expr != NULL && IsA(tle->expr, SetToDefault))
+	{
+		type_id = attrtype;
+		isDefault = true;
+	}
+
+	/* Otherwise the expression holds the type */
+	else
+		type_id = exprType((Node *) tle->expr);
+
 	/*
 	 * If there are subscripts on the target column, prepare an array
 	 * assignment expression.  This will generate an array value that the
@@ -383,7 +400,7 @@ updateTargetListEntry(ParseState *pstate,
 		 * coercion.  But accept InvalidOid, which indicates the source is
 		 * a NULL constant.  (XXX is that still true?)
 		 */
-		if (type_id != InvalidOid)
+		if (!isDefault && type_id != InvalidOid)
 		{
 			tle->expr = (Expr *)
 				coerce_to_target_type(pstate,

src/backend/rewrite/rewriteHandler.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.120 2003/05/02 20:54:35 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.121 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -307,7 +307,25 @@ rewriteTargetList(Query *parsetree, Relation target_relation)
 			{
 				Assert(strcmp(resdom->resname,
 							  NameStr(att_tup->attname)) == 0);
-				new_tle = process_matched_tle(old_tle, new_tle);
+
+				if (old_tle->expr != NULL && IsA(old_tle->expr, SetToDefault))
+				{
+					/* Set to the default value of the column, as requested */
+					Node	   *new_expr;
+
+					new_expr = build_column_default(target_relation, attrno);
+
+					new_tle = makeTargetEntry(makeResdom(attrno,
+														 att_tup->atttypid,
+														 att_tup->atttypmod,
+											  pstrdup(NameStr(att_tup->attname)),
+														 false),
+											  (Expr *) new_expr);
+				}
+				else
+					/* Normal Case */
+					new_tle = process_matched_tle(old_tle, new_tle);
+
 				/* keep scanning to detect multiple assignments to attr */
 			}
 		}

src/include/nodes/nodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: nodes.h,v 1.141 2003/06/25 03:40:19 momjian Exp $
+ * $Id: nodes.h,v 1.142 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -277,7 +277,7 @@ typedef enum NodeTag
 	T_PrivGrantee,
 	T_FuncWithArgs,
 	T_PrivTarget,
-	T_InsertDefault,
+	T_SetToDefault,
 	T_CreateOpClassItem,
 	T_CompositeTypeStmt,
 	T_InhRelation,

src/include/nodes/parsenodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.239 2003/06/25 03:40:19 momjian Exp $
+ * $Id: parsenodes.h,v 1.240 2003/06/25 04:19:24 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -279,10 +279,10 @@ typedef struct ResTarget
 /*
  * Empty node used as a marker for Default Columns
  */
-typedef struct InsertDefault
+typedef struct SetToDefault
 {
 	NodeTag		type;
-} InsertDefault;
+} SetToDefault;
 
 /*
  * SortGroupBy - for ORDER BY clause