The question mark is a special character that represents the Unknown value. ABL treats a quoted question mark ("?") in a procedure or an input field as a question mark character. It treats an unquoted question mark (?) in a procedure or an input field as an unknown value.
The following table indicates the results when using the Unknown value (?) in a comparison expression (EQ, GE, GT, LE, LT, NE). These results are true for both character and integer variables.
Comparison operator | One argument is ? | Both arguments are ? |
---|---|---|
EQ or = | F | T |
GE or >= | ? | T |
GT or > | ? | F |
LE or <= | ? | T |
LT or < | ? | F |
NE or <> | T | F |
Additional points about the Unknown value (?) are:
For information on how the Unknown value (?) works with logical data types, comparison operators, and conditional statements, see the following reference entries: EQ or = operator, GE or >= operator, GT or > operator, IF...THEN...ELSE statement, LE or < = operator, LT or < operator, NE or <> operator