Question

Is there a way to specify a mysql query that does something like this

SELECT * FROM a LEFT JOIN b ON (a.xyz = b.xyz OR a.xyr = b.xyr);

and therefore returns rows when any of the LEFT JOIN criteria on the ON statement matches up…

if so what would be the syntax of such queries?

Answer 1

Split the select statement into two parts and use a UNION.

SELECT * FROM a LEFT JOIN b on a.xyz = b.xyz
UNION
SELECT * FROM a LEFT JOIN b on a.xyr = b.xyr

If the UNION in MySQL is like the UNION in SQL Server, it should produce a set without duplicate rows. Otherwise, you may need to use a DISTINCT.