what is the use of composite key constraint?

Question Posted / zikku

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what is the use of composite key constraint?..

Answer / deva

its used to create a primary keys based on two or more
columns in the particular table.

By the set, those should be unique.

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what is the use of composite key constraint?..

Answer / 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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