Re: a union is always a join!

From: <compdb_at_hotmail.com>
Date: Thu, 29 Jan 2009 21:05:18 -0800 (PST)
Message-ID: <55c69eca-1566-4e6e-8e3a-f02456ae6cc0_at_p36g2000prp.googlegroups.com>



On Jan 29, 2:05 pm, com..._at_hotmail.com wrote:

> R MINUS (for permitted R and Q) Q is also R OR Q.

R UNION Q (for permitted R and Q) is R OR Q.

> Eg R add C as A-B means R COMPOSE (PLUS rename ARG1 as C, ARG2 as B,
> RESULT as A)

Eg R add A-B as C means R JOIN (PLUS rename ARG1 as C, ARG2 as B, RESULT as A)
Eg R add A+B as C means R JOIN (PLUS rename ARG1 as A, ARG2 as B, RESULT as C)

philip Received on Thu Jan 29 2009 - 23:05:18 CST

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