self join using report generator

[reportmaker]

I have a requirement to extract two field values from the customfieldvalues table for all the clients. The table stores the custom fields values with the clients numbers. How can i join the table by itself to extract values for two fields in the report generator or can it be done by only using custom php code without the report generator.

I have tried joining the clients table with the table customfieldvalues and then by itself.It displays table alias error.

[reportmaker]

Thanks for the reply I want to make this report using report generator module .but it is giving table alias error because i cant have two tables with the same name .