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