Re: relational algrabra division?
From: ruben safir <ruben_at_mrbrklyn.com>
Date: Fri, 12 Dec 2014 02:33:22 -0500
Message-ID: <m6e5ns$f1a$1_at_reader1.panix.com>
Date: Fri, 12 Dec 2014 02:33:22 -0500
Message-ID: <m6e5ns$f1a$1_at_reader1.panix.com>
On 12/11/2014 09:13 PM, James K. Lowden wrote:
>> > (e) Retrieve the names of employees who work on every project
> That kind!
in deed. With enough scotch I can understand this
There is this line in the text about division :(
The DIVISION operation can be expressed as a sequence of π, ×, and –
operations as
follows:
T1 ← πY(R)
T2 ← πY((S × T1) – R)
T ← T1 – T2
tried this and go some insite but it is still just magic Received on Fri Dec 12 2014 - 08:33:22 CET