Predicates are truth-tests. If the predicate test is true, it returns a value. Each predicate is evaluated per row so that when the predicate is part of an entire table SELECT statement, the statement can return multiple results.
Predicates consist of a set of parameters and arguments. For example, in the following example WHERE clause:
WHERE name = ‘Smith’;
- name = ‘Smith’ is the predicate
- ‘Smith’ is an expression
Predicates can be achieved using:
- BETWEEN Operator
- EXISTS Operator
- IN Operator
- LIKE Operator
- Search condition statements
Querona provides the following predicates.
IS [NOT] NULL¶
Determines whether a specified expression is NULL.
expression IS [ NOT ] NULL
expression Is any valid expression.
NOT Specifies that the Boolean result has to be negated. The predicate reverses its return values, returning TRUE if the value is not NULL, and FALSE if the value is NULL.