How to address field names in a join query

I have 3 tables with some fields with the same name. For example:

TABLE_A: PR_CODE, DESCRIPTION, IS_VALID

TABLE_B: PR_ST_CODE, PR_CODE, DESCRIPTION

TABLE_C: PR_VD_CODE, PR_CODE, DESCRIPTION

As you see, the DESCRIPTION field is present in all tables.
Now suppose i want to do query like this:

select * from (table_a a inner join table_b b on a.pr_code = b.pr_code) x
inner join table_c c on x.pr_code = c.pr_code

I obtain a resultset with these fields:
PR_CODE | DESCRIPTION | IS_VALID | PR_ST_CODE | DESCRIPTION | PR_VD_CODE |
DESCRIPTION

The question is: how can i refer to the fields DESCRIPTION of each table?

I can refer to table_c DESCRIPTION with c.DESCRIPTION but if i write
x.DESCRIPTION postgresql cannot identy the true field names because
actually there are two x.DESCRIPTION fields... How can i refer to these?

Sorry for the english, I hope you understand anyway...

Doct. Eng. Denis
Gasparin denis(at)edistar(dot)com
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Administrator http://www.edistar.com
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