PLSQL_基础系列02_分组函数GROUP BY / ROLLUP / CUBE（案例）-优快云博客

2014-11-30 Created By BaoXinjian

一、摘要

ROLLUP 运算符生成的结果集类似于 CUBE 运算符生成的结果集。

1. 下面是 CUBE 和 ROLLUP 之间的具体区别：

CUBE 生成的结果集显示了所选列中值的所有组合的聚合。

ROLLUP 生成的结果集显示了所选列中值的某一层次结构的聚合。

2. ROLLUP 优点：

(1). ROLLUP 返回单个结果集，而 COMPUTE BY 返回多个结果集，而多个结果集会增加应用程序代码的复杂性。

(2). ROLLUP 可以在服务器游标中使用，而 COMPUTE BY 则不可以。

(3). 有时，查询优化器为 ROLLUP 生成的执行计划比为 COMPUTE BY 生成的更为高效。

二、创建测试数据

1. 创建资料

CREATE TABLE DEPARTMENT
(
   DEPARTMENT   CHAR (10),
   EMPLOYEE     CHAR (6),
   SALARY       INT
);
 
BEGIN
 INSERT INTO DEPARTMENT SELECT 'A','ZHANG',100 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'A','LI',   200 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'A','WANG', 300 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'A','ZHAO', 400 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'A','DUAN', 500 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'B','DUAN', 600 FROM DUAL;
 INSERT INTO DEPARTMENT SELECT 'B','DUAN', 700 FROM DUAL;
END;