Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!mrspoc!itkin
From: itkin@mrspoc.Transact.COM (Steven M. List)
Newsgroups: comp.databases
Subject: Re: Unify SQL Problem
Message-ID: <1991Feb16.020641.17376@mrspoc.Transact.COM>
Date: 16 Feb 91 02:06:41 GMT
References: <6973@emory.mathcs.emory.edu>
Reply-To: steven@Transact.COM
Distribution: usa
Organization: Transact Software
Lines: 24

cheung@mathcs.emory.edu (Shun Yan Cheung) writes:

>Does Unify's SQL has the EXISTS function ? I am getting errors in the
>WHERE clause when I try to use the EXISTS clause. If not, what can I
>do to reformulate the query ? I suspect using the COUNT() = 0 test might
>work, but I have a hard time reformulating it. The query I am looking
>into is: Find all employees with no dependents (Query 6 from Elmasri 
>and Navathe's book on page 187). The relevant relations are:
>
>	EMPLOYEE(SSN, FNAME, LNAME, ....)
>	DEPENDENT(ESSN, ....)
>
>where ESSN is a foreign key of the EMPLOYEE relation. Any clues ?

select fname, lname, ssn
from employee
where 0 = select count(*) from dependent where
	dependent.essn = employee.essn

-- 
 +----------------------------------------------------------------------------+
 :                Steven List @ Transact Software, Inc. :^>~                  :
 :           Chairman, Unify User Group of Northern California                :
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