slightly more paranoid database schema:.

made column 'program' in table 'versions' be not null, and unique.
optimally you would want a unique index on 'value' and 'program' but
indexes are not supported on datatype 'tinytext' until mysql 3.23

webtools/bugzilla/checksetup.pl

@@ -735,8 +735,9 @@ $table{fielddefs} =
 
 $table{versions} =
    'value tinytext,
-    program varchar(64)';
+    program varchar(64) not null,
 
+    unique(program)';
 
 $table{votes} =
    'who mediumint not null,