How to create primary key constraints in oracle

A primary key is a special column or combination of columns that uniquely identifies each row in a table. It ensures that the records in the table are unique and can be created by specifying the table name using the ALTER TABLE statement. Add the PRIMARY KEY keyword followed by the column name to specify as the primary key. Primary key constraints help ensure data uniqueness, improve query speeds, prevent duplicate records and simplify table joins.

Create primary key constraints using Oracle

The role of primary key

A primary key is a special column or combination of columns that uniquely identifies each row in the table. It ensures that each record in the table is unique and that records can be found quickly and efficiently.

Syntax for creating primary key constraints

 <code class="oracle">ALTER TABLE table_name ADD PRIMARY KEY (column_name1, column_name2, ...);</code>

in:

• table_name is the table name to create the primary key constraint.
• column_name1 , column_name2 , ... are the columns to be specified as primary key.

Example

To create a primary key constraint for a table named employees , the primary key column is employee_id :

 <code class="oracle">ALTER TABLE employees ADD PRIMARY KEY (employee_id);</code>

Benefits of primary key constraints

Creating primary key constraints has some major benefits:

• Ensure uniqueness of data in the table.
• Improve data query and retrieval speed.
• Prevents repeated records from being inserted.
• Simplify table connection and data manipulation operations.

Things to note

• The primary key column cannot be NULL.
• Primary key constraints can only be applied to columns with unique values.
• It cannot be deleted after creating a primary key constraint unless the table is empty.

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