Database Reference
In-Depth Information
▼
Input
SELECT COUNT(*) AS num_cust
FROM customers;
▼
Output
+----------+
| num_cust |
+----------+
| 5 |
+----------+
▼
Analysis
In this example,
COUNT(*)
is used to count all rows, regardless of values. The
count is returned in
num_cust
.
The following example counts just the customers with an e-mail address:
▼
Input
SELECT COUNT(cust_email) AS num_cust
FROM customers;
▼
Output
+----------+
| num_cust |
+----------+
| 3 |
+----------+
▼
Analysis
This
SELECT
statement uses
COUNT(cust_email)
to count only rows with a value
in the
cust_email
column. In this example,
cust_email
is
3
(meaning that only
three of the five customers have e-mail addresses).
Note
NULL
Values Column rows with
NULL
values in them are ignored by the
COUNT()
function if a column name is specified, but not if the asterisk (
*
) is used.
MAX()
returns the highest value in a specified column.
MAX()
requires that the
column name be specified, as seen here:
