SQL | DESCRIBE Statement

Prerequisite : Sql Create Clause,

As the name suggests, DESCRIBE is used to describe something. Since in database we have tables, that’s why we use DESCRIBE or DESC(both are same) command to describe the structure of a table.
Syntax:

DESCRIBE one;
  OR
DESC one;

Note : We can use either DESCRIBE or DESC(both are Case Insensitive).

Suppose our table whose name is one has 3 columns named FIRST_NAME, LAST_NAME and SALARY and all are of can contain null values.

Output:

Name          Null       Type
FIRST_NAME              CHAR(25)
LAST_NAME               CHAR(25)
SALARY                  NUMBER(6)

• Here, above on using DESC or either DESCRIBE we are able to see the structure of a table but not on the console tab, the structure of table is shown in the describe tab of the Database System Software.
• So desc or describe command shows the structure of table which include name of the column, data-type of column and the nullability which means, that column can contain null values or not.
• All of these features of table are described at the time of Creation of table.

Example :

Creating table or defining the structure of a table

create table one
(
id int not null, 
name char(25)
)

Here, we created a table whose name is one and its columns are ID, NAME and the id is of not null type i.e, we can’t put null values in the ID column but we can put null values in the NAME column.

Example to demonstrate DESC:

Step 1: Defining structure of table i.e, Creating a table:

create table one
(
 id int not null,
 name char(25),
 city varchar2(25)
)

Step 2: Displaying the structure of table:

DESC one
  OR
DESCRIBE one

Output:
Name      Null       Type
ID       Not Null    INT
NAME                CHAR(25)
CITY                VARCHAR2(25)

Note: Here above ID column is of not null type and rest 2 column can contain null values.

Note: You have to execute DESC command on your system software only, because this command won’t run on any editor. Make sure to run this command on your own installed Database only

References: Oracle.com

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