MySQL Bugs: #68902: Duplicate table aliases

Bug #68902	Duplicate table aliases
Submitted:	9 Apr 2013 12:16	Modified:	9 Apr 2013 17:00
Reporter:	Ammon Sutherland	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Parser	Severity:	S3 (Non-critical)
Version:	5.1, 5.5, 5.0.97, 5.1.70, 5.5.32, 5.6.12, 5.7.1	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	duplicate alias

Description:
Under certain conditions MySQL allows for using duplicate table aliases.  Requirements seem to be that the tables are in different databases and no column name is referenced which might be duplicated in both tables.

How to repeat:
CREATE DATABASE test1;
CREATE TABLE test1.t1 (a INT(1));
INSERT INTO test1.t1 VALUES(1);

CREATE DATABASE test2;
CREATE TABLE test2.t2 (b INT(1));
INSERT INTO test2.t2 VALUES(2);

SELECT * FROM test1.t1 tba;
+------+
| a    |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

SELECT * FROM test2.t2 tba;
+------+
| b    |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

SELECT
   tba.a,
   tba.b
FROM
   test1.t1 tba
   JOIN test2.t2 tba;

Suggested fix:
Depends if this is a "feature" or an actual bug.  Right now it's allowed but can be considered pretty bad style.

Thank you for the report.

Verified as described.