ALTER TABLE DROP COLUMN works. Patch by Christopher Kings-Lynne,

code review by Tom Lane.  Remaining issues: functions that take or
return tuple types are likely to break if one drops (or adds!)
a column in the table defining the type.  Need to think about what
to do here.

Along the way: some code review for recent COPY changes; mark system
columns attnotnull = true where appropriate, per discussion a month ago.

src/backend/utils/cache/lsyscache.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.76 2002/07/12 18:43:18 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/lsyscache.c,v 1.77 2002/08/02 18:15:08 tgl Exp $
  *
  * NOTES
  *	  Eventually, the index information should go through here, too.
@@ -115,16 +115,15 @@ get_attname(Oid relid, AttrNumber attnum)
  *
  *		Given the relation id and the attribute name,
  *		return the "attnum" field from the attribute relation.
+ *
+ *		Returns InvalidAttrNumber if the attr doesn't exist (or is dropped).
  */
 AttrNumber
-get_attnum(Oid relid, char *attname)
+get_attnum(Oid relid, const char *attname)
 {
 	HeapTuple	tp;
 
-	tp = SearchSysCache(ATTNAME,
-						ObjectIdGetDatum(relid),
-						PointerGetDatum(attname),
-						0, 0);
+	tp = SearchSysCacheAttName(relid, attname);
 	if (HeapTupleIsValid(tp))
 	{
 		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
@@ -166,32 +165,6 @@ get_atttype(Oid relid, AttrNumber attnum)
 		return InvalidOid;
 }
 
-/* This routine uses the attname instead of the attnum because it
- * replaces the routine find_atttype, which is called sometimes when
- * only the attname, not the attno, is available.
- */
-bool
-get_attisset(Oid relid, char *attname)
-{
-	HeapTuple	tp;
-
-	tp = SearchSysCache(ATTNAME,
-						ObjectIdGetDatum(relid),
-						PointerGetDatum(attname),
-						0, 0);
-	if (HeapTupleIsValid(tp))
-	{
-		Form_pg_attribute att_tup = (Form_pg_attribute) GETSTRUCT(tp);
-		bool		result;
-
-		result = att_tup->attisset;
-		ReleaseSysCache(tp);
-		return result;
-	}
-	else
-		return false;
-}
-
 /*
  * get_atttypmod
  *

src/backend/utils/cache/syscache.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/syscache.c,v 1.84 2002/07/25 10:07:12 ishii Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/cache/syscache.c,v 1.85 2002/08/02 18:15:08 tgl Exp $
  *
  * NOTES
  *	  These routines allow the parser/planner/executor to perform
@@ -622,6 +622,71 @@ GetSysCacheOid(int cacheId,
 	return result;
 }
 
+
+/*
+ * SearchSysCacheAttName
+ *
+ * This routine is equivalent to SearchSysCache on the ATTNAME cache,
+ * except that it will return NULL if the found attribute is marked
+ * attisdropped.  This is convenient for callers that want to act as
+ * though dropped attributes don't exist.
+ */
+HeapTuple
+SearchSysCacheAttName(Oid relid, const char *attname)
+{
+	HeapTuple	tuple;
+
+	tuple = SearchSysCache(ATTNAME,
+						   ObjectIdGetDatum(relid),
+						   CStringGetDatum(attname),
+						   0, 0);
+	if (!HeapTupleIsValid(tuple))
+		return NULL;
+	if (((Form_pg_attribute) GETSTRUCT(tuple))->attisdropped)
+	{
+		ReleaseSysCache(tuple);
+		return NULL;
+	}
+	return tuple;
+}
+
+/*
+ * SearchSysCacheCopyAttName
+ *
+ * As above, an attisdropped-aware version of SearchSysCacheCopy.
+ */
+HeapTuple
+SearchSysCacheCopyAttName(Oid relid, const char *attname)
+{
+	HeapTuple	tuple,
+				newtuple;
+
+	tuple = SearchSysCacheAttName(relid, attname);
+	if (!HeapTupleIsValid(tuple))
+		return tuple;
+	newtuple = heap_copytuple(tuple);
+	ReleaseSysCache(tuple);
+	return newtuple;
+}
+
+/*
+ * SearchSysCacheExistsAttName
+ *
+ * As above, an attisdropped-aware version of SearchSysCacheExists.
+ */
+bool
+SearchSysCacheExistsAttName(Oid relid, const char *attname)
+{
+	HeapTuple	tuple;
+
+	tuple = SearchSysCacheAttName(relid, attname);
+	if (!HeapTupleIsValid(tuple))
+		return false;
+	ReleaseSysCache(tuple);
+	return true;
+}
+
+
 /*
  * SysCacheGetAttr
  *