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The PostgreSQL ALTER TABLE order is utilized to add, erase or adjust sections in a current table. 

You would likewise utilize ALTER TABLE order to add and drop different imperatives on a current table. 

Syntax

The fundamental grammar of ALTER TABLE to add another segment in a current table is as per the following − 

ALTER TABLE table_name ADD column_name datatype;

The fundamental grammar of ALTER TABLE to DROP COLUMN in a current table is as per the following − 

ALTER TABLE table_name DROP COLUMN column_name;

The essential sentence structure of ALTER TABLE to change the DATA TYPE of a section in a table is as per the following − 

ALTER TABLE table_name ALTER COLUMN column_name TYPE datatype;

The essential linguistic structure of ALTER TABLE to add a NOT NULL requirement to a section in a table is as per the following − 

ALTER TABLE table_name MODIFY column_name datatype NOT NULL;

The essential language structure of ALTER TABLE to ADD UNIQUE CONSTRAINT to a table is as per the following − 

ALTER TABLE table_name
ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...);

The essential language structure of ALTER TABLE to ADD CHECK CONSTRAINT to a table is as per the following − 

ALTER TABLE table_name
ADD CONSTRAINT MyUniqueConstraint CHECK (CONDITION);

The essential punctuation of ALTER TABLE to ADD PRIMARY KEY requirement to a table is as per the following − 

ALTER TABLE table_name
ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...);

The essential language structure of ALTER TABLE to DROP CONSTRAINT from a table is as per the following − 

ALTER TABLE table_name
DROP CONSTRAINT MyUniqueConstraint;

In the event that you are utilizing MySQL, the code is as per the following − 

ALTER TABLE table_name
DROP INDEX MyUniqueConstraint;

The essential punctuation of ALTER TABLE to DROP PRIMARY KEY requirement from a table is as per the following − 

ALTER TABLE table_name
DROP CONSTRAINT MyPrimaryKey;

In the event that you are utilizing MySQL, the code is as per the following − 

ALTER TABLE table_name
DROP PRIMARY KEY;

Example

Consider our COMPANY table has the accompanying records − 

 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Allen |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000

Coming up next is the guide to ADD another section in a current table − 

testdb=# ALTER TABLE COMPANY ADD GENDER char(1);

Presently, COMPANY table is changed and the accompanying would be the yield from SELECT proclamation − 

 id | name  | age | address     | salary | gender
----+-------+-----+-------------+--------+--------
  1 | Paul  |  32 | California  |  20000 |
  2 | Allen |  25 | Texas       |  15000 |
  3 | Teddy |  23 | Norway      |  20000 |
  4 | Mark  |  25 | Rich-Mond   |  65000 |
  5 | David |  27 | Texas       |  85000 |
  6 | Kim   |  22 | South-Hall  |  45000 |
  7 | James |  24 | Houston     |  10000 |
(7 rows)

Coming up next is the guide to DROP sex section from existing table − 

testdb=# ALTER TABLE COMPANY DROP GENDER;

Presently, COMPANY table is changed and the accompanying would be the yield from SELECT articulation − 

 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Allen |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000