Hi All,
Greetings of the day!
Today we will explore what is difference between the primary key & the unique key in the database, so let's start.
Primary Key
- Each table can have only one primary key.
- The primary key will create a clustered index.
- The primary key can be related to other tables as a Foreign Key.
- The primary key can not have null values
Unique Key
- Each table can have multiple unique keys.
- The unique key will create a non clustered unique index.
- A unique key can have one null value.
- A unique key cannot be related to other tables as a foreign key.
Now let's see how we can declare the primary key & unique key in oracle.
CREATE TABLE STUDENT (
STUDNET_ID NUMBER,
STUDENT_NAME VARCHAR(20),
STUDENT_MOBILE_NO NUMBER,
CONSTRAINT "STUDNET_ID_PK" PRIMARY KEY(STUDNET_ID),
CONSTRAINT "STUDENT_MOBILE_NO" UNIQUE(STUDENT_MOBILE_NO)
);
Now let's see the difference between clustered & non clustered indexes.
Clustered Index
- The clustered index defines orders in which data is physically sorted in a table.
- There can be only one clustered index in the table since data in the table can be sorted in only one order.
Non-Clustered Index
- Non clustered index is a separate index used for maintaining uniqueness or improving performance.
- There can be multiple non clustered indexes in a table.
Thank you
Happy Learning!
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