Question

I’ve got some SQL that used to work with an older MySQL version, but after upgrading to a newer MySQL 5 version, I’m getting an error. Here’s the SQL:

SELECT portfolio.*, projects.*, types.*
FROM projects, types
LEFT JOIN portfolio
ON portfolio.pfProjectID = projects.projectID
WHERE projects.projectType = types.typeID AND types.typeID = #URL.a#
ORDER BY types.typeSort, projects.projectPriority ASC

and the new error I’m receiving:

Unknown column 'projects.projectID' in 'on clause'

How can I convert this to compatible SQL for the newer MySQL version?

Thanks very much!

Answer 1

You need to rewrite the query using INNER JOIN instead of comma operator:

SELECT portfolio.*, projects.*, types.*
FROM projects
INNER JOIN types
ON projects.projectType = types.typeID
LEFT JOIN portfolio
ON portfolio.pfProjectID = projects.projectID
WHERE types.typeID = #URL.a#
ORDER BY types.typeSort, projects.projectPriority ASC

Explanation:

This has to do with MySQL changing operator precedence to comply with ANSI standards. Check out the MySQL documentation: http://dev.mysql.com/doc/refman/5.1/en/join.html

INNER JOIN and , (comma) are
semantically equivalent in the absence
of a join condition: both produce a
Cartesian product between the
specified tables (that is, each and
every row in the first table is joined
to each and every row in the second
table).

However, the precedence of the comma
operator is less than of INNER JOIN,
CROSS JOIN, LEFT JOIN, and so on. If
you mix comma joins with the other
join types when there is a join
condition, an error of the form
Unknown column ‘col_name’ in ‘on
clause’ may occur. Information about
dealing with this problem is given
later in this section.

There is also more detailed explanation on MySQL page, search for “Previously, the comma operator (,)”