SQLite

<verbatim>
$ sqlite3
SQLite version 3.6.18
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> CREATE TABLE a (a INTEGER);
sqlite> CREATE TABLE b (a INTEGER);
sqlite> CREATE TABLE c (a INTEGER);
sqlite> SELECT * FROM a JOIN b USING (a);
sqlite> SELECT * FROM a JOIN b USING (a) JOIN c USING (a);
sqlite> SELECT * FROM a JOIN b USING (a) WHERE a = 1;
sqlite> SELECT * FROM a JOIN b USING (a) JOIN c USING (a) WHERE a = 1;
SQL error: ambiguous column name: a
sqlite> 
</verbatim>

This bug was found while working on a class table inheritance plugin for the Sequel Ruby ORM.

<hr><i>drh added on 2011-10-13 14:44:54:</i><br>
The column name is ambiguous.  Does it mean a.a or b.a?  The result is the
same either way, but I don't expect the parser to know this.