ALTER COMMAND

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MySQL - Alter Command

The ALTER command is used to modify the existing table.
It involves adding,removing,modifying,creating,dropping,renaming,changing the engine,changing the collation of table or some columns.

SYNTAX :

ALTER TABLE table_name
  ADD new_column_name column_definition
    [ FIRST | AFTER column_name ];

Lets consider a table and check how alter command is performing :

ID	Name	Address	Company	Salary
1	Nihari	Habsiguda	DELL	25000
2	Swara	Madhapur	HCL	35000
3	Lara	SR nagar	XIUS	54000
4	Kiara	KPHB	GOOGLE	64000
5	Harshad	Gachibowli	HP	48000

Adding a new column :

ALTER TABLE employeerecord
  ADD Gender varchar(55) NOT NULL
    AFTER Salary;

Result will be displayed as follows:

ID	Name	Address	Company	Salary	Gender
1	Nihari	Habsiguda	DELL	25000	-

Removing a column from the existing table:

ALTER TABLE employeerecord DROP Column Gender;

Result will be displayed as follows:

ID	Name	Address	Company	Salary
1	Nihari	Habsiguda	DELL	25000

Modifying the data type, name, default values of a column in the existing table :

ALTER TABLE  employeerecord
CHANGE COLUMN Salary  Compensation
Int(55) NOT NULL;  

Result will be displayed as follows :

ID	Name	Address	Company	Compensation
1	Nihari	Habsiguda	DELL	25000