Re: Unable To Alter Data Type

-----Original Message-----
From: pgsql-sql-owner(at)postgresql(dot)org [mailto:pgsql-sql-owner(at)postgresql(dot)org]
On Behalf Of Carlos Mennens
Sent: Wednesday, January 11, 2012 6:53 PM
To: PostgreSQL (SQL)
Subject: [SQL] Unable To Alter Data Type

Now I'm attempting to ALTER the field 'cust_zip' TYPE from character to
integer however I'm getting the following error:

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I think there is a rule in PostgreSQL that says that any field with "zip" in
the name MUST BE of a character type :)

You seriously do not want to turn this into an integer (big or otherwise) -
ZIP (POSTAL) CODES ARE NOT NUMERIC; THEY ARE TEXT!

If someone is telling you to make this change then tell them they are wrong
and whatever requirement are in place on the other end need to be modified -
not the table you indicate.

I do confirm, however, that a direct cast from character to bigint works and
thus you SHOULD be able to perform the TYPE alteration without adding the
USING (expression) clause. So either this is a bug OR, more likely,
character-to-bigint casting is not implicit (or an assignment cast, whatever
that is) and so you must resort to the USING clause - which does work.

[ ... ALTER COLUMN zip_code TYPE bigint USING (zip_code::bigint) ]

http://www.postgresql.org/docs/9.0/interactive/sql-altertable.html

This is on 9.0 for me.

However, I will say again, you DO NOT WANT TO ACTUALLY DO THIS!

The specific issue is that some US Postal Code begin with a zero ( 0 ) and
so whenever you want to the zip_code value you need to pad leading zeros if
the length is less than 5. Now consider that a full zip_code can be in 5+4
format with an embedded hyphen and you no longer can even store it as
numeric. If you deal with Canada (and maybe Mexico) at all then spaces and
letters become acceptable characters within the zip_code.

David J.