Description
The NOT EQUAL (!=) operator tests whether two values are not equal.
Usage
a != b
Remarks
The value of the expression is TRUE if the two values are not equal, and FALSE if they are.
Generally, a and b must have the same type. That is, a and b must both be numbers, or text, or dates. However, if either a or b are of different types, but one is text, then the other will be implicitly converted to text using the same conventions as the TEXT function.
When comparing text, the comparison is case sensitive. That means that "ABC" does not equal "abc".
Examples
Avoid duplicate phone numbers
If your form has both a field for a FIXED_LINE_PHONE_NUMBER and a MOBILE_NUMBER, you may want to ensure that two distinct numbers are provided.
In this case, you could add a validation rule for the MOBILE_NUMBER field like:
FIXED_LINE_PHONE_NUMBER != MOBILE_NUMBER
This will ensure that duplicate phone numbers are not provided.