How to modify the field type and name using SQL alter

How to modify the field type and name using SQL alter

Alter table "table_name"
[Change method]

ADD a column: ADD "column 1" "column 1 data type"

Mysql tutorial> create table Employee (
-> Id int,
-> First_name VARCHAR (15 ),
-> Last_name VARCHAR (15 ),
-> Start_date DATE,
-> End_date DATE,
-> Salary FLOAT (8, 2 ),
-> City VARCHAR (10 ),
-> Description VARCHAR (15)
-> );
Query OK, 0 rows affected (0.03 sec)

Mysql>
Mysql>
Mysql> alter table employee
-> CHANGE First_Name FirstName VARCHAR (20 );
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

Mysql>
Mysql> DESCRIBE employee;
+ ------------- + ------ + ----- + --------- + ------- +
| Field | Type | Null | Key | Default | Extra |
+ ------------- + ------ + ----- + --------- + ------- +
| Id | int (11) | YES | NULL |
| FirstName | varchar (20) | YES | NULL |
| Last_name | varchar (15) | YES | NULL |
| Start_date | date | YES | NULL |
| End_date | date | YES | NULL |
| Salary | float (8, 2) | YES | NULL |
| City | varchar (10) | YES | NULL |
| Description | varchar (15) | YES | NULL |
+ ------------- + ------ + ----- + --------- + ------- +
8 rows in set (0.01 sec)

Change Field to varchar type

Mysql> alter table employee
-> CHANGE Last_Name VARCHAR (50 );
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0

Add an index to a field

Mysql> alter table myTable
-> Add unique (OrderID, ModelID );
Query OK, 0 rows affected (0.06 sec)