Sometimes we need to change the data type of a column. To do this, we use the ALTER TABLE Modify Column command. For Oracle and MySQL, the SQL syntax for ALTER TABLE Modify Column is,

ALTER TABLE "table_name"
MODIFY "column 1" "New Data Type"

For SQL Server, the syntax is,

ALTER TABLE "table_name"
ALTER COLUMN "column 1" "New Data Type"

Let's look at the example. Assuming our starting point is the "customer" table created in the CREATE TABLE section:

Table customer

Column Name	Data Type
First_Name	char(50)
Last_Name	char(50)
Address	char(50)
City	char(50)
Country	char(25)
Birth_Date	date

Our goal is to alter the data type of the "Address" column to char(100). To do this, we key in:

MySQL:
ALTER TABLE customer MODIFY Address char(100);

Oracle:
ALTER TABLE customer MODIFY Address char(100);

SQL Server:
ALTER TABLE customer ALTER COLUMN Address char(100);

Resulting table structure:

Table customer

Column Name	Data Type
First_Name	char(50)
Last_Name	char(50)
Address	char(100)
City	char(50)
Country	char(25)

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