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From: lape@cs.utk.edu (Bryon S. Lape)
Newsgroups: comp.databases
Subject: Computer columns in R:BASE 3.1
Message-ID: <1991Mar1.004311.11605@cs.utk.edu>
Date: 1 Mar 91 00:43:11 GMT
Sender: usenet@cs.utk.edu (USENET News Poster)
Organization: University of Tennessee, Knoxville - CS Department
Lines: 30
Originator: lape@hydra2c.cs.utk.edu


	I need to have a computed column be a result of a WHERE clause type
cross table reference.  Or in simpler terms....

	Say table Letter_Grades have two columns like so:

		Letter		Number
	       ----------    ------------
		   A+		 4.00
		   A		 4.00
		   A-		 3.67
		   .		  .
		   .		  .
		   F		 0.00

	Now another table holds grades for a student.  Those grades are
entered by a letter, but I need to compute the quality points (credit hours
* grade) by looking up the corresponding Letter ==> Number grade.  I have
tried something like this:

		ENGL1011
	      ------------

		(Number IN Letter_Grades WHERE Letter = ENGL1011)

	but this causes the column to be test field holding the above
string.  Is what I need impossible???


Bryon Lape