Answer Posted / srikanth
A composite key is used to club primary key for more than
once column.
PRIMARY KEY(<<COLUMN1>>,<<COLUMN2>>....<<COLUMNN>>)
But the disadvantage is that it will allow duplicates for
any one of the fields.
Example:
CREATE TABLE Example1
(Id INT NOT NULL,Pername VARCHAR(20) NULL,Phno INT NOT NULL
PRIMARY KEY(Id,Phno)
)
Command(s) completed successfully.
INSERT INTO Example1
VALUES(1,'sri',1111)
(1 row(s) affected)
INSERT INTO Example1
VALUES(1,'sri',6666)
(1 row(s) affected)
SELECT * FROM Example1
Id Pername Phno
1 sri 1111
1 sri 6666
As you can see that it is allowing same Id.
Basically Composite Key will take all the fields defined as
a group.So it is least bothered about any one of the field.
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