Comparison Operators v13
The usual comparison operators are shown in the following table:
Operator | Description |
---|---|
< | Less than |
> | Greater than |
<= | Less than or equal to |
>= | Greater than or equal to |
= | Equal |
<> | Not equal |
!= | Not equal |
Comparison operators are available for all data types where this makes sense. All comparison operators are binary operators that return values of type BOOLEAN;
expressions like 1 < 2 < 3
are not valid (because there is no <
operator to compare a Boolean value with 3
).
In addition to the comparison operators, the special BETWEEN
construct is available.
a BETWEEN x AND y
is equivalent to
a >= x AND a <= y
Similarly,
a NOT BETWEEN x AND y
is equivalent to
a < x OR a > y
There is no difference between the two respective forms apart from the CPU cycles required to rewrite the first one into the second one internally.
To check whether a value is or is not null, use the constructs
expression IS NULL
expression IS NOT NULL
Do not write expression = NULL
because NULL
is not "equal to" NULL
. (The null value represents an unknown value, and it is not known whether two unknown values are equal.) This behavior conforms to the SQL standard.
Some applications may expect that expression = NULL
returns true if expression
evaluates to the null value. It is highly recommended that these applications be modified to comply with the SQL standard.