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Course:
Research Note Topic:
Research Note Description:
The 8 operators for Codd’s relational algebra are :
Restriction
Projection
Product
Union
Intersection
Difference
Join
Division
Defination and examples of the 8 operators :
TABLE1 :SUPPLIERS
S
SName
Status
City
S1
Smith
20
London
S2
Jones
10
Paris
S3
Blake
30
Paris
S4
Clark
20
London
S5
Adams
30
Athens
TABLE2 :PARTS
P
PName
Color
Weight
City
P1
Nut
Red
12
London
P2
Bolt
Green
17
Paris
P3
Screw
Blue
17
Rome
P4
Screw
Red
14
London
P5
Cam
Blue
12
Paris
P6
Cog
Red
19
London
TABLE3 :SHIPMENTS
S
P
Quantity
S4
P2
200
S3
P2
200
S2
P2
400
S2
P1
300
S1
P6
100
S1
P4
200
S1
P3
400
S4
P5
400
S4
P4
300
S1
P2
200
S1
P1
300
Restriction :
Returns a table containing all records from a specified table that satisfy a specific condition.
Query :
select * from shipments where Quantity<150;
Projection :
Returns a table containing all (sub) records that remain in a specified fields have been removed.
Query :
select S, City from suppliers;
Product :
Returns a table containing all possible records that are a combination of two records, one from each of two specified tables.
Query :
select * from suppliers, parts where suppliers.S = "S1" and parts.P = "P1";
Union :
Returns a table containing all records that appear in either or both of two specified tables.
Query :
select * from suppliers, parts where suppliers.S = parts.P union select *from suppliers, parts where suppliers.S<>parts.P;
Intersection :
Returns a table containing all records that appear in both of two specified tables.
Query :
select * from suppliers, parts where suppliers.S = parts.P;
Difference :
Returns a table containing all records that appear in both of two specified tables.
Query :
still searching .
Join :
Returns a table containing all possible records that are a combination of two records one from each of two specified tables, such that the two records contributing to any given combination have a common value for the common fields of the two tables (and that common value appears just once, not twice in the resulting record).
Query :
select suppliers.S, SName, Status, City, P, Quantity from suppliers, shipments where suppliers.S = shipments.S;
Division :
Takes two single-field tables and one double-field table and returns a table containing all records from one single-field table that appear in the double-field table matched with all records in the other single-field table.
Query :
still searching .
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Prof. Ashay Dharwadker