如何理解Oracle分組函數(shù)的ROLLUP，針對(duì)這個(gè)問(wèn)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(wèn)題的小伙伴找到更簡(jiǎn)單易行的方法。
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通過(guò)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(jiǎn)用法，這里同時(shí)給出ROLLUP的Group By的改寫(xiě)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(yǔ)句翻譯一下上面的SQL語(yǔ)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(yǔ)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(lái)什么效果了么？
有的同學(xué)還是沒(méi)有看出來(lái)，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(méi)有理解清楚，請(qǐng)參見(jiàn)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(guò)程中帶來(lái)極大的便利，而且效率比起來(lái)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)。
關(guān)于如何理解Oracle分組函數(shù)的ROLLUP問(wèn)題的解答就分享到這里了，希望以上內(nèi)容可以對(duì)大家有一定的幫助，如果你還有很多疑惑沒(méi)有解開(kāi)，可以關(guān)注創(chuàng)新互聯(lián)行業(yè)資訊頻道了解更多相關(guān)知識(shí)。
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