Orcale SQL Tutorial


Primary Key

Primary Key

In Oracle, Primary key is the column which has unique values, and it cannot be null. In a table, there can be only one primary key.

Primary Key - Using CREATE TABLE statement

Syntax:

  1. CREATE TABLE table_name  
  2. (  
  3.   column1 datatype null/not null,  
  4.   column2 datatype null/not null,  
  5.   ...  
  6.   CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n)  
  7. );  

 

Example

  1. CREATE TABLE Test2(ID Number, NAME Varchar2 CONSTRAINT test2_pk PRIMARY KEY (ID));  

 

Primary Key in Oracle

Primary Key - Using ALTER TABLE statement

Syntax:

  1. ALTER TABLE table_name  
  2. ADD CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n);  

 

Example

  1. ALTER TABLE student ADD CONSTRAINT student_pk PRIMARY KEY(id);  

 

Primary Key in Oracle Using Alter Table

Drop Primary Key

Syntax:

  1. ALTER TABLE table_name  
  2. DROP CONSTRAINT constraint_name;  

 

Example

  1. ALTER TABLE student DROP CONSTRAINT student_pk ; 

 

Primary Key in Oracle Drop Primary Key

Disable Primary Key

Syntax:

  1. ALTER TABLE table_name  
  2. DISABLE CONSTRAINT constraint_name;  

 

Example

  1. ALTER TABLE student DISABLE CONSTRAINT student_pk ;  

 

Primary Key in Oracle Disable Primary Key

Enable Primary Key

Syntax:

  1. ALTER TABLE table_name  
  2. ENABLE CONSTRAINT constraint_name;  

 

Example

  1. ALTER TABLE student ENABLE CONSTRAINT student_pk ;  

Primary Key in Oracle Enable Primary Key

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