MySQL Bugs: #15065: The usage advisor sometimes reports a referenced column as unreferenced

Bug #15065	The usage advisor sometimes reports a referenced column as unreferenced
Submitted:	19 Nov 2005 9:22	Modified:	23 Nov 2005 5:15
Reporter:	Yuan WANG	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / J	Severity:	S3 (Non-critical)
Version:	3.1.11	OS:	Windows (WinXP)
Assigned to:	Mark Matthews	CPU Architecture:	Any

Description:
I set the usage advisor flag of the JDBC connection to find out unreferenced columns return by queries in my application. However, I find that the usage advisor sometimes makes false statements that some columns have not been referenced, even through they' re indeed. Here is a simple test.
			((com.mysql.jdbc.Connection)conn).setUseUsageAdvisor(true);
			java.sql.Statement stmt = conn.createStatement();
			java.sql.ResultSet rs = stmt.executeQuery("select count(*) from t1 limit 1");
			rs.next();
			System.out.println("T1 has " + rs.getInt(1) + " rows");
			rs.close();
Where "conn" is the connection to the database and "t1" can be any table. While runing the test above, the JDBC driver will report "The following columns were  part of the SELECT statement for this result set, but were never referenced: .count(*)". This is simply wrong.

How to repeat:
Connection to any database and execute the following.
			((com.mysql.jdbc.Connection)conn).setUseUsageAdvisor(true);
			java.sql.Statement stmt = conn.createStatement();
			java.sql.ResultSet rs = stmt.executeQuery("select count(*) from t1 limit 1");
			rs.next();
			System.out.println("T1 has " + rs.getInt(1) + " rows");
			rs.close();
Where "conn" is the connection to the database and "t1" can be any table.

Thanks for the bug report. I was able to reproduce the bug. I would like to notice that I had java.lang.NullPointerException with any query. My test case is attached.

Test case

Attachment: Bug15065.java (text/java), 1002 bytes.

Fixed for 3.1.12  and 5.0.0. See nightly snapshot from http://downloads.mysql.com/snapshots.php#connector-j after 00:00 GMT Nov 24th, or subversion repository at http://svn.mysql.com/svnpublic/connector-j/branches/branch_3_1 immediately (i.e. build from source) for the fix.

Thanks for the bug report.

I still see this sometimes with 5.0.4. I cannot create a reproducible test case.