Logical functions allow to differentiate from one case to the other. There are three fundamental elements:
- if / then / else,
- logical references.
The construct ( if a then b else c ) checks first, if condition a is correct. If it is, it will calculate b, else c.
As a condition you need an expression which returns Yes / No. That can be:
- a Yes / No field,
- a comparison,
- a logical reference.
- (if Yes then 1 else 2) always will return 1
- (if No then 1 else 2) always will return 2
- (if Age >= 18 then “of full age” else”minor”)
Comparisons always return a Yes / No value.
(a = b) a equal b
(a ≠ b) a unequal b
(a < b) a less than b
(a ≤ b) a lass than or equal b
(a ≥ b) a greater than or equal b
(a > b) a greater than b
(a like b) textual comparison between a and b where capital letters and several special charactersare ignored.
Using logical combination you can construct more complex conditions. They need a Yes / No value as an argument and return a Yes / No value as well.
Yes the constant value Yes
No the constant value No
(a and b) results in Yes, if a as well as b are Yes – else No.
(a oder b) results in Yes, if a or b or both are Yes – else No.
(not a) results in Yes, if b is No – else No.