On next code you can see that
on dbbase command CALCULATE COUNT(expression)
( CALCULATE is 4 X faster respect to a SELECT !)
is correct when expression is a numeric,
for a not numeric expression, it fire a error

CREATE CURSOR aaa ( ax i NULL,ay L NULL)
INSERT INTO aaa values(NULL,NULL)
INSERT INTO aaa values(0,.F.)
CALCULATE COUNT(AX) TO SS
? SS && 1, as it must be
* next fire a sum error
CALCULATE COUNT(AY) TO SS