Database Reference
In-Depth Information
Input
CREATE TABLE orders
(
order_num int NOT NULL AUTO_INCREMENT,
order_date datetime NOT NULL ,
cust_id int NOT NULL ,
PRIMARY KEY (order_num)
) ENGINE=Aria;
Analysis
This statement creates the orders table used throughout this topic. orders
contains three columns: order number, order date, and the customer ID. All
three columns are required, and so each contains the keyword NOT NULL . This
prevents the insertion of columns with no value. If someone tries to insert no
value, an error will be returned, and the insertion will fail.
This next example creates a table with a mixture of NULL and NOT NULL
columns:
Input
CREATE TABLE vendors
(
vend_id int NOT NULL AUTO_INCREMENT,
vend_name char(50) NOT NULL ,
vend_address char(50) NULL ,
vend_city char(50) NULL ,
vend_state char(5) NULL ,
vend_zip char(10) NULL ,
vend_country char(50) NULL ,
PRIMARY KEY (vend_id)
) ENGINE=Aria;
Analysis
This statement creates the vendors table used throughout this topic. The ven-
dor ID and vendor name columns are both required, and are, therefore, speci-
fied as NOT NULL . The five remaining columns all allow NULL values, and so
NOT NULL is not specified. NULL is the default setting, so if NOT NULL is not
specified, NULL is assumed.
 
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