SQL Alter methods to modify field types and names
ALTER TABLE "table_name"
[Change Mode]
Add a field: Add "Field 1" "Field 1 Data category"
MySQL Tutorials > CREATE TABLE Employee (
-> id int,
-> first_ name VARCHAR,
-> last_name VARCHAR,
-> start_date Date,
-> end_date date,
-> salary FLOAT (8,2),
-> city VARCHAR (Ten),
-> description VARCHAR (a)
->);
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)
Modify field varchar type
mysql> ALTER TABLE Employee
-> Change last_name 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)