Date: 03/16/07 (MySQL Communtiy)    Keywords: mysql, sql

Wiki tells me:

In mathematics, the cardinality of a set is a measure of the "number of elements of the set".

Keyname      Type      Cardinality    Field
infant       INDEX     1              infant

mysql> SELECT DISTINCT(infant) FROM table;
+----------+
|  infant  |
+----------+
| NULL     |
| A        |
| B        |
| C        |
| U        |
+----------+
5 rows in set (0.09 sec)

Source: http://community.livejournal.com/mysql/111487.html