This article is about comparison operators as part of the SQL syntax that USoft supports.
Comparison operators
In a condition with a comparison operator, the expression to the left of the operator is compared to the expression to the right. The outcome is a truth value: True or False.
| a is equal to b |
| a is not equal to b |
| a is greater than b |
| a is greater than or equal to b |
| a is smaller than b |
| a is smaller or equal to b |
| a is not equal to b |
| a is equal to the NULL value |
| a is not equal to the NULL value |
The != and <> operators are equivalent. They both return True if the expressions evaluate to a different value and False if they evaluate to the same value.
A number value is greater than another number value if it is greater in the mathematical sense. A string value is greater than another string value if it is comes last in alphabetical sort order. A date value is greater than another date/time value if it designates a later date/time.
NULL values
Comparisons with a NULL value evaluate to False, regardless of the mathematical operator.
This is a source of errors when working with relational databases generally, but especially in a USoft context, because comparisons with NULL will cause a constraint not to have an effect.
Best practice in USoft applications is to keep non-mandatory columns (columns where NULLs are allowed) to an absolute minimum.
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