COUNT is a set function.

· COUNT(*) supplies the total number of values (rows in a result table or group).

· COUNT(DISTINCT <expression>)supplies the total number of different values (number of values in the argument of the DISTINCT function).

· COUNT(ALL <expression>)supplies the number of values that differ from the NULL value (number of values in the argument of the ALL function)

The result has the data type FIXED(10).

Example table: customer

How many customers are there?

SELECT COUNT (*) number FROM customer

number |

15 |