COUNT is an aggregate function
Derby Reference Manual
123
The specified number is the angle, in radians, that you want the cotangens for. The
specified number must be a
· If the specified number is NULL, the result of this function is NULL.
Syntax
COT ( number )
COUNT function
COUNT is an aggregate function that counts the number of rows accessed in an
expression (see
). COUNT is allowed on all types of
expressions.
Syntax
COUNT ( [ DISTINCT | ALL ] Expression )
The DISTINCT qualifier eliminates duplicates. The ALL qualifier retains duplicates. ALL
is assumed if neither ALL nor DISTINCT is specified. For example, if a column contains
the values 1, 1, 1, 1, and 2, COUNT(col) returns a greater value than COUNT(DISTINCT
col).
Only one DISTINCT aggregate expression per
the following query is not allowed:
-- query not allowed
SELECT COUNT (DISTINCT flying_time), SUM (DISTINCT miles)
FROM Flights
An Expression can contain multiple column references or expressions, but it cannot
contain another aggregate or subquery. If an Expression evaluates to NULL, the
aggregate is not processed for that value.
The resulting data type of COUNT is
Example
-- Count the number of countries in each region,
-- show only regions that have at least 2
SELECT COUNT (country), region
FROM Countries
GROUP BY region
HAVING COUNT (country) > 1
COUNT(*) function
COUNT(*) is an aggregate function that counts the number of rows accessed. No NULLs
or duplicates are eliminated. COUNT(*) does not operate on an expression.
Syntax
COUNT(*)
The resulting data type is
.
Example
-- Count the number of rows in the Flights table
SELECT COUNT(*)
FROM Flights
