范围规则

范围规则使用 SQL 关系和逻辑运算符来定义表中每个分段的边界。范围规则可包含运算符的以下有限集合：

关系运算符 >、<、>= 和 <=
逻辑运算符 AND 和 OR
包含内置函数的代数表达式

如以下示例所示，范围规则可以基于简单的代数表达式。在该示例中，表达式是对某一列的简单引用。

   FRAGMENT BY EXPRESSION
id_num > 0  AND id_num <= 20 IN dbsp1,
id_num > 20 AND id_num <= 40 IN dbsp2,
id_num > 40 IN dbsp3

按照范围规则的表达式可以是多个代数表达式的逻辑乘或逻辑和。下一个示例显示了用来定义两组范围的两个代数表达式。第一组范围基于代数表达式：“YEAR(Died) - YEAR(Born)”；第二组范围基于“MONTH(Born)”。

   FRAGMENT BY EXPRESSION
YEAR(Died) - YEAR(Born) < 21 AND MONTH(Born) >= 1  AND MONTH(Born) < 4 IN dbsp1,
YEAR(Died) - YEAR(Born) < 40 AND MONTH(Born) >= 4  AND MONTH(Born) <  7 IN dbsp2,