Saturday, July 23, 2011

Alter Table Modify Column Syntax


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 TABLEsection:
Table customer
Column NameData Type
First_Namechar(50)
Last_Namechar(50)
Addresschar(50)
Citychar(50)
Countrychar(25)
Birth_Datedate

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 NameData Type
First_Namechar(50)
Last_Namechar(50)
Addresschar(100)
Citychar(50)
Countrychar(25)



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