Fix ALTER TABLE to check pre-existing NOT NULL constraints when rewriting

a table.  Otherwise a USING clause that yields NULL can leave the table
violating its constraint (possibly there are other cases too).  Per report
from Alexander Pravking.

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.192 2006/07/03 22:45:38 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.193 2006/07/10 22:10:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -123,6 +123,7 @@ typedef struct AlteredTableInfo
 	/* Information saved by Phases 1/2 for Phase 3: */
 	List	   *constraints;	/* List of NewConstraint */
 	List	   *newvals;		/* List of NewColumnValue */
+	bool		new_notnull;	/* T if we added new NOT NULL constraints */
 	Oid			newTableSpace;	/* new tablespace; 0 means no change */
 	/* Objects to rebuild after completing ALTER TYPE operations */
 	List	   *changedConstraintOids;	/* OIDs of constraints to rebuild */
@@ -132,11 +133,11 @@ typedef struct AlteredTableInfo
 } AlteredTableInfo;
 
 /* Struct describing one new constraint to check in Phase 3 scan */
+/* Note: new NOT NULL constraints are handled elsewhere */
 typedef struct NewConstraint
 {
 	char	   *name;			/* Constraint name, or NULL if none */
-	ConstrType	contype;		/* CHECK, NOT_NULL, or FOREIGN */
-	AttrNumber	attnum;			/* only relevant for NOT_NULL */
+	ConstrType	contype;		/* CHECK or FOREIGN */
 	Oid			refrelid;		/* PK rel, if FOREIGN */
 	Node	   *qual;			/* Check expr or FkConstraint struct */
 	List	   *qualstate;		/* Execution state for CHECK */
@@ -2438,7 +2439,7 @@ ATRewriteTables(List **wqueue)
 			 * Test the current data within the table against new constraints
 			 * generated by ALTER TABLE commands, but don't rebuild data.
 			 */
-			if (tab->constraints != NIL)
+			if (tab->constraints != NIL || tab->new_notnull)
 				ATRewriteTable(tab, InvalidOid);
 
 			/*
@@ -2504,6 +2505,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 	TupleDesc	oldTupDesc;
 	TupleDesc	newTupDesc;
 	bool		needscan = false;
+	List	   *notnull_attrs;
 	int			i;
 	ListCell   *l;
 	EState	   *estate;
@@ -2554,9 +2556,6 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 			case CONSTR_FOREIGN:
 				/* Nothing to do here */
 				break;
-			case CONSTR_NOTNULL:
-				needscan = true;
-				break;
 			default:
 				elog(ERROR, "unrecognized constraint type: %d",
 					 (int) con->contype);
@@ -2572,6 +2571,25 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 		ex->exprstate = ExecPrepareExpr((Expr *) ex->expr, estate);
 	}
 
+	notnull_attrs = NIL;
+	if (newrel || tab->new_notnull)
+	{
+		/*
+		 * If we are rebuilding the tuples OR if we added any new NOT NULL
+		 * constraints, check all not-null constraints.  This is a bit of
+		 * overkill but it minimizes risk of bugs, and heap_attisnull is
+		 * a pretty cheap test anyway.
+		 */
+		for (i = 0; i < newTupDesc->natts; i++)
+		{
+			if (newTupDesc->attrs[i]->attnotnull &&
+				!newTupDesc->attrs[i]->attisdropped)
+				notnull_attrs = lappend_int(notnull_attrs, i);
+		}
+		if (notnull_attrs)
+			needscan = true;
+	}
+
 	if (needscan)
 	{
 		ExprContext *econtext;
@@ -2672,6 +2690,17 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 			ExecStoreTuple(tuple, newslot, InvalidBuffer, false);
 			econtext->ecxt_scantuple = newslot;
 
+			foreach(l, notnull_attrs)
+			{
+				int		attn = lfirst_int(l);
+
+				if (heap_attisnull(tuple, attn+1))
+					ereport(ERROR,
+							(errcode(ERRCODE_NOT_NULL_VIOLATION),
+							 errmsg("column \"%s\" contains null values",
+									NameStr(newTupDesc->attrs[attn]->attname))));
+			}
+
 			foreach(l, tab->constraints)
 			{
 				NewConstraint *con = lfirst(l);
@@ -2685,21 +2714,6 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 									 errmsg("check constraint \"%s\" is violated by some row",
 											con->name)));
 						break;
-					case CONSTR_NOTNULL:
-						{
-							Datum		d;
-							bool		isnull;
-
-							d = heap_getattr(tuple, con->attnum, newTupDesc,
-											 &isnull);
-							if (isnull)
-								ereport(ERROR,
-										(errcode(ERRCODE_NOT_NULL_VIOLATION),
-								 errmsg("column \"%s\" contains null values",
-										get_attname(tab->relid,
-													con->attnum))));
-						}
-						break;
 					case CONSTR_FOREIGN:
 						/* Nothing to do here */
 						break;
@@ -3398,7 +3412,6 @@ ATExecSetNotNull(AlteredTableInfo *tab, Relation rel,
 	HeapTuple	tuple;
 	AttrNumber	attnum;
 	Relation	attr_rel;
-	NewConstraint *newcon;
 
 	/*
 	 * lookup the attribute
@@ -3434,13 +3447,8 @@ ATExecSetNotNull(AlteredTableInfo *tab, Relation rel,
 		/* keep the system catalog indexes current */
 		CatalogUpdateIndexes(attr_rel, tuple);
 
-		/* Tell Phase 3 to test the constraint */
-		newcon = (NewConstraint *) palloc0(sizeof(NewConstraint));
-		newcon->contype = CONSTR_NOTNULL;
-		newcon->attnum = attnum;
-		newcon->name = "NOT NULL";
-
-		tab->constraints = lappend(tab->constraints, newcon);
+		/* Tell Phase 3 it needs to test the constraint */
+		tab->new_notnull = true;
 	}
 
 	heap_close(attr_rel, RowExclusiveLock);
@@ -3909,7 +3917,6 @@ ATExecAddConstraint(AlteredTableInfo *tab, Relation rel, Node *newConstraint)
 								newcon = (NewConstraint *) palloc0(sizeof(NewConstraint));
 								newcon->name = ccon->name;
 								newcon->contype = ccon->contype;
-								newcon->attnum = ccon->attnum;
 								/* ExecQual wants implicit-AND format */
 								newcon->qual = (Node *)
 									make_ands_implicit((Expr *) ccon->expr);