DBS DBS lecture 2 Relations and relational algebra 1.0 / 5 based on 1 rating ? ComputingOtherAll boards Created by: Samantha BinghamCreated on: 04-05-09 12:27 Relation A set of pairs 1 of 6 Degree of a relation How long the tuples are or how many columns the table has 2 of 6 Cardinality of the relation How many different tuples there are or how many different rows the table has 3 of 6 Union {a,b,c} U {a,d,e} = {a,b,c,d,e} In order to take a union of relations R and S, R and S must have the same number of columns and the corresponding columns must have the same domains 4 of 6 Intersection {a,b,c,d} n {a,d,e,f} = {a,d} Intersection is a relation R n S which contains tuples which are in both R and S 5 of 6 Projection π 2 (R) takes the 2nd column from table R 6 of 6
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