Database Reference
In-Depth Information
▼
Output
+----------------+------------+
| prod_name | prod_price |
+----------------+------------+
| .5 ton anvil | 5.99 |
| 1 ton anvil | 9.99 |
| Bird seed | 10.00 |
| Oil can | 8.99 |
| TNT (5 sticks) | 10.00 |
+----------------+------------+
▼
Analysis
As seen in this example, when
BETWEEN
is used, two values must be
specified—the low end and high end of the desired range. The two values must
also be separated by the
AND
keyword.
BETWEEN
matches all the values in the
range, including the specified range start and end values.
When a table is created, the table designer can specify whether individual col-
umns can contain no value. When a column contains no value, it is said to
contain a
NULL
value.
New Term
NULL
No value
, as opposed to a field containing
0
, or an empty string, or just
spaces.
To determine if a value is
NULL
, you cannot simply check to see if
= NULL
.
Instead, the
SELECT
statement has a special
WHERE
clause that can be used to
check for columns with
NULL
values—the
IS NULL
clause. The syntax looks
like this:
▼
Input
SELECT prod_name
FROM products
WHERE prod_price IS NULL;
This statement returns a list of all products that have no price (an empty
prod_price
field, not a price of
0
), and because there are none, no data is
returned. The
customers
table, however, does contain columns with
NULL
values—the
cust_email
column contains
NULL
if a customer has no e-mail
address on file:
