A composite key is a combination of
two or more columns in a table that can be used to uniquely identify each row
in the table. As we know if we want to make any changes on the existing table
we need to use Alter commend.
Let’s see how to create composite
primary key on my existing table.
There is no any key on this table.
With the help of alter we can create the key.
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ALTER TABLE EMP_SOURCE
ADD CONSTRAINT PK_EMP_SOURCE
PRIMARY KEY (EMP_ID,EMP_NAME,EMP_ADD)
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PK is created successfully.
NOTE:
when we are creating composite primary key keep in mind composite column should
be not null. If there is any column null in this case it will throw an error as
below.
