oracle primary key | Primary Key - oracle tutorial - sql tutorial



Oracle create table with only primary key

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What is oracle primary key ?

  • A primary key is a single field or combination of fields that uniquely defines a record.
  • A primary key column cannot contain NULL values.
  • Most tables should have a primary key, and each table can have only ONE primary key.
  • Oracle primary key

    Oracle primary key and foreign key

Syntax:

CREATE TABLE table_name
(
  column1 datatype null/not null,
  column2 datatype null/not null,
  ...

  CONSTRAINT constraint_name PRIMARY KEY (column1, column2, ... column_n)
);
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Oracle constrains primary key

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Example:

CREATE TABLE wikitechy_emp(
emp_id number(1) PRIMARY KEY,
emp_name varchar(20),
emp_designation varchar(20))
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Creating Primary key in the Table:

 Oracle primary key query
  1. In the create table statement, PRIMARY KEY constraint is applied for emp_id column.
 Oracle primary key insert query
  • We are inserting id value 1, name value as ARUN and designation value as project manager into a wikitechy_emp table using insert into keyword.
 Oracle primary key insert query with another values
  • Here, when we insert a same value for emp_id which you have already inserted in your first row. The unique constraint (PRIMARY KEY) reject your insertion of data into the wikitechy_emp table and shows a violated message.

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