如何理解Oracle分組函數(shù)的ROLLUP

如何理解Oracle分組函數(shù)的ROLLUP，針對(duì)這個(gè)問題，這篇文章詳細(xì)介紹了相對(duì)應(yīng)的分析和解答，希望可以幫助更多想解決這個(gè)問題的小伙伴找到更簡單易行的方法。

通過演示給出Oracle ROLLUP分組函數(shù)的用法，體驗(yàn)一下Oracle在統(tǒng)計(jì)查詢領(lǐng)域中的函數(shù)魅力。ROLLUP分組函數(shù)可以理解為Group By分組函數(shù)封裝后的精簡用法，這里同時(shí)給出ROLLUP的Group By的改寫思路。

1.初始化實(shí)驗(yàn)壞境
1）創(chuàng)建測(cè)試表group_test
SECOOLER@ora11g> create table group_test (group_id int, job varchar2(10), name varchar2(10), salary int);

Table created.

2）初始化數(shù)據(jù)
insert into group_test values (10,'Coding',    'Bruce',1000);
insert into group_test values (10,'Programmer','Clair',1000);
insert into group_test values (10,'Architect', 'Gideon',1000);
insert into group_test values (10,'Director',  'Hill',1000);

insert into group_test values (20,'Coding',    'Jason',2000);
insert into group_test values (20,'Programmer','Joey',2000);
insert into group_test values (20,'Architect', 'Martin',2000);
insert into group_test values (20,'Director',  'Michael',2000);

insert into group_test values (30,'Coding',    'Rebecca',3000);
insert into group_test values (30,'Programmer','Rex',3000);
insert into group_test values (30,'Architect', 'Richard',3000);
insert into group_test values (30,'Director',  'Sabrina',3000);

insert into group_test values (40,'Coding',    'Samuel',4000);
insert into group_test values (40,'Programmer','Susy',4000);
insert into group_test values (40,'Architect', 'Tina',4000);
insert into group_test values (40,'Director',  'Wendy',4000);

commit;

3）初始化之后的數(shù)據(jù)情況如下：
SECOOLER@ora11g> set pages 100
SECOOLER@ora11g> select * from group_test;

  GROUP_ID JOB        NAME           SALARY
---------- ---------- ---------- ----------
        10 Coding     Bruce            1000
        10 Programmer Clair            1000
        10 Architect  Gideon           1000
        10 Director   Hill             1000
        20 Coding     Jason            2000
        20 Programmer Joey             2000
        20 Architect  Martin           2000
        20 Director   Michael          2000
        30 Coding     Rebecca          3000
        30 Programmer Rex              3000
        30 Architect  Richard          3000
        30 Director   Sabrina          3000
        40 Coding     Samuel           4000
        40 Programmer Susy             4000
        40 Architect  Tina             4000
        40 Director   Wendy            4000

16 rows selected.

2.先看一下普通分組的效果：對(duì)group_id進(jìn)行普通的group by操作---按照小組進(jìn)行分組
SECOOLER@ora11g> select group_id,sum(salary) from group_test group by group_id;

  GROUP_ID SUM(SALARY)
---------- -----------
        30       12000
        20        8000
        40       16000
        10        4000

3.對(duì)group_id進(jìn)行普通的roolup操作---按照小組進(jìn)行分組，同時(shí)求總計(jì)
SECOOLER@ora11g> select group_id,sum(salary) from group_test group by rollup(group_id);

  GROUP_ID SUM(SALARY)
---------- -----------
        10        4000
        20        8000
        30       12000
        40       16000
                 40000

  使用Group By語句翻譯一下上面的SQL語句如下（union all一個(gè)統(tǒng)計(jì)所有數(shù)據(jù)的行）：
SECOOLER@ora11g> select group_id,sum(salary) from group_test group by group_id
  2  union all
  3  select null, sum(salary) from group_test
  4  order by 1;

  GROUP_ID SUM(SALARY)
---------- -----------
        10        4000
        20        8000
        30       12000
        40       16000
                 40000

4.再看一個(gè)rollup兩列的情況
SECOOLER@ora11g> select group_id,job,sum(salary) from group_test group by rollup(group_id, job);

  GROUP_ID JOB        SUM(SALARY)
---------- ---------- -----------
        10 Coding            1000
        10 Director          1000
        10 Architect         1000
        10 Programmer        1000
        10                   4000
        20 Coding            2000
        20 Director          2000
        20 Architect         2000
        20 Programmer        2000
        20                   8000
        30 Coding            3000
        30 Director          3000
        30 Architect         3000
        30 Programmer        3000
        30                  12000
        40 Coding            4000
        40 Director          4000
        40 Architect         4000
        40 Programmer        4000
        40                  16000
                            40000

21 rows selected.

上面的SQL語句該如何使用Group By進(jìn)行翻譯呢？
答案如下：
SECOOLER@ora11g> select group_id,job,sum(salary) from group_test group by group_id, job
  2  union all
  3  select group_id,null,sum(salary) from group_test group by group_id
  4  union all
  5  select null,null,sum(salary) from group_test
  6  order by 1,2;

  GROUP_ID JOB        SUM(SALARY)
---------- ---------- -----------
        10 Architect         1000
        10 Coding            1000
        10 Director          1000
        10 Programmer        1000
        10                   4000
        20 Architect         2000
        20 Coding            2000
        20 Director          2000
        20 Programmer        2000
        20                   8000
        30 Architect         3000
        30 Coding            3000
        30 Director          3000
        30 Programmer        3000
        30                  12000
        40 Architect         4000
        40 Coding            4000
        40 Director          4000
        40 Programmer        4000
        40                  16000
                            40000

21 rows selected.

5.補(bǔ)充一步，體驗(yàn)一下GROUPING函數(shù)的效果
直接看效果就OK啦：
SECOOLER@ora11g> select group_id,job,grouping(GROUP_ID),grouping(JOB),sum(salary) from group_test group by rollup(group_id, job);

  GROUP_ID JOB        GROUPING(GROUP_ID) GROUPING(JOB) SUM(SALARY)
---------- ---------- ------------------ ------------- -----------
        10 Coding                      0             0        1000
        10 Director                    0             0        1000
        10 Architect                   0             0        1000
        10 Programmer                  0             0        1000
        10                             0             1        4000
        20 Coding                      0             0        2000
        20 Director                    0             0        2000
        20 Architect                   0             0        2000
        20 Programmer                  0             0        2000
        20                             0             1        8000
        30 Coding                      0             0        3000
        30 Director                    0             0        3000
        30 Architect                   0             0        3000
        30 Programmer                  0             0        3000
        30                             0             1       12000
        40 Coding                      0             0        4000
        40 Director                    0             0        4000
        40 Architect                   0             0        4000
        40 Programmer                  0             0        4000
        40                             0             1       16000
                                       1             1       40000

21 rows selected.

  看出來什么效果了么？
  有的同學(xué)還是沒有看出來，小小的解釋一下：
  如果顯示“1”表示GROUPING函數(shù)對(duì)應(yīng)的列（例如JOB字段）是由于ROLLUP函數(shù)所產(chǎn)生的空值對(duì)應(yīng)的信息，即對(duì)此列進(jìn)行匯總計(jì)算后的結(jié)果。
  如果顯示“0”表示此行對(duì)應(yīng)的這列參未與ROLLUP函數(shù)分組匯總活動(dòng)。
  如果還是沒有理解清楚，請(qǐng)參見Oracle官方文檔中的描述內(nèi)容：“Using a single column as its argument, GROUPING returns 1 when it encounters a NULL value created by a ROLLUP or CUBE operation. That is, if the NULL indicates the row is a subtotal, GROUPING returns a 1. Any other type of value, including a stored NULL, returns a 0.”

6.小結(jié)
  ROLLUP在數(shù)據(jù)統(tǒng)計(jì)和報(bào)表生成過程中帶來極大的便利，而且效率比起來Group By + Union組合方法效率高得多。這也體現(xiàn)了Oracle在SQL統(tǒng)計(jì)分析上人性化、自動(dòng)化、高效率的特點(diǎn)。

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