Oracle Topics

CREATE TABLE in Oracle
In Oracle, CREATE TABLE statement is used to create a new table in the database. To create a table, you have to name that table and define its columns and datatype for each column.

Syntax:- 
  

    CREATE TABLE table_name  
    (   
      column1 datatype [ NULL | NOT NULL ],  
      column2 datatype [ NULL | NOT NULL ],  
      ...  
      column_n datatype [ NULL | NOT NULL ]  
    );

Note:- In Oracle, total number of columns cannot be more than 32.

Explanation:- table_name:- It specifies the name of the table which you want to create.

column1, column2, ... column n:- It specifies the columns which you want to add in the table. Every column must have a datatype. Every column should either be defined as "NULL" or "NOT NULL". In the case, the value is left blank; it is treated as "NULL" as default.

Oracle CREATE TABLE Example:- Here we are creating a table named customers. This table doesn't have any primary key. 
  

    CREATE TABLE customers  
    ( customer_id number(10) NOT NULL,  
      customer_name varchar2(50) NOT NULL,  
      city varchar2(50)  
    );


Explanation of above table customers
customer_id:- It is the first column created as a number datatype (maximum 10 digits in length) and cannot contain null values.
customer_name:- it is the second column created as a varchar2 datatype (50 maximum characters in length) and cannot contain null values.
city:- This is the third column created as a varchar2 datatype. It can contain null values.

Oracle CREATE TABLE Example with primary key:- 
  

    CREATE TABLE customers  
    ( customer_id number(10) NOT NULL,  
      customer_name varchar2(50) NOT NULL,  
      city varchar2(50),  
      CONSTRAINT customers_pk PRIMARY KEY (customer_id)  
    );


Now, question is that What is Primary key:-
A primary key is a single field or combination of fields that contains a unique record.
It must be filled. None of the field of primary key can contain a null value.
A table can have only one primary key.