Add a new column in postgresql

To add a new column in PostgreSQL, you can use the ALTER TABLE command. Here is the basic syntax:

ALTER TABLE table_name ADD COLUMN new_column_name data_type;

Here:

• table_name is the name of the table you want to modify.
• new_column_name is the name of the new column you want to add.
• data_type is the data type of the new column (e.g. integer, varchar, text, etc.).

For example, to add a new column called age with a data type of integer to a table called employees, you would use the following command:

ALTER TABLE employees ADD COLUMN age integer;

This will add a new column called age with a data type of integer to the employees table.

You can also specify additional options, such as:

• DEFAULT value: specifies the default value for the new column.
• NOT NULL constraint: specifies that the new column cannot be null.
• UNIQUE constraint: specifies that the new column must have a unique value.

For example:

ALTER TABLE employees ADD COLUMN age integer DEFAULT 25 NOT NULL;

This will add a new column called age with a data type of integer, a default value of 25, and a NOT NULL constraint.

Note that you can only add a new column to the end of the table. If you want to add a new column in a specific position, you can use the ALTER TABLE command with the ADD COLUMN clause and specify the position of the new column using the AFTER or BEFORE keyword. For example:

ALTER TABLE employees ADD COLUMN new_column_name integer AFTER existing_column_name;

This will add a new column called new_column_name with a data type of integer after the existing_column_name column.

Also, you can use the ALTER TABLE command with the ADD COLUMN clause and specify the position of the new column using the POSITION keyword. For example:

ALTER TABLE employees ADD COLUMN new_column_name integer POSITION 2;

This will add a new column called new_column_name with a data type of integer at the 2nd position in the table.

It's important to note that when you add a new column to a table, it will not affect the existing data in the table. The new column will be added with a default value of NULL for all existing rows.