It is evaluated whether the checked value gets into the certain range. For doing this you can use BETWEEN…AND instruction. It checks whether the source value is between two given values. There are three expressions in such condition. The first expression defines the checked value; the second and the third ones define the upper and the low limits of the range. The checked expression can be any legal one, often it is the field name. The rules for NULL values processing in BETWEEN…AND check:

If the expression defining the upper range limit has NULL value, BETWEEN check returns FALSE, when the checked value is less than the low range limit, and NULL in the opposite case. Note. BETWEEN…AND instruction is not widening the SQL possibilities as it can be expressed as two comparisons:

A BETWEEN B AND C

fully equivalent:

(A >= B) AND (A <= C)

But BETWEEN…AND instruction is the more simple way to express the selection condition in the value range terms.