目錄

• 1. 認(rèn)識分析函數(shù)
• 1.1 什么是分析函數(shù)
• 1.2 分析函數(shù)和聚合函數(shù)的不同
• 1.3 分析函數(shù)的形式
• 2. 理解over()函數(shù)
• 2.1 兩個order by 的執(zhí)行機制
• 2.2 分析函數(shù)中的分組、排序、窗口
• 2.3 幫助理解over()的實例
• 3. 常見分析函數(shù)
• 3.1 演示表和數(shù)據(jù)的生成
• 3.2 first_value()與last_value():求最值對應(yīng)的其他屬性
• 3.3 rank()、dense_rank()與row_number() 排序問題
• 3.4 lag()與lead():求之前或之后的第N行
• 3.5 rollup()與cube()：排列組合分組
• 3.6 max()、min()、sum()與avg()：求移動的最值、總和與平均值
• 3.7 ratio_to_report()：求百分比
• 總結(jié)

1. 認(rèn)識分析函數(shù)

1.1 什么是分析函數(shù)

分析函數(shù)是Oracle專門用于解決復(fù)雜報表統(tǒng)計需求的功能強大的函數(shù)，它可以在數(shù)據(jù)中進行分組然后計算基于組的某種統(tǒng)計值，并且每一組的每一行都可以返回一個統(tǒng)計值。

1.2 分析函數(shù)和聚合函數(shù)的不同

普通的聚合函數(shù)用group by分組，每個分組返回一個統(tǒng)計值；而分析函數(shù)采用partition by 分組，并且每組每行都可以返回一個統(tǒng)計值。

1.3 分析函數(shù)的形式

分析函數(shù)帶有一個開窗函數(shù)over(),包含三個分析子句：分組(partition by)，排序(order by), 窗口(rows)，他們的使用形式如下：

over(partition by xxx  order by yyy rows between zzz)-- 例如在scott.emp表中：xxx為deptno, yyy為sal, -- zzz為unbounded preceding and unbounded following

分析函數(shù)的例子：

顯示各部門員工的工資，并附帶顯示該部分的最高工資。

SQL如下：

SELECT DEPTNO, EMPNO, ENAME, SAL, LAST_VALUE(SAL) OVER (PARTITION BY DEPTNO ORDER BY SAL ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) MAX_SAL FROM EMP;

結(jié)果為：

注： current row 表示當(dāng)前行

unbounded preceding 表示第一行

unbounded following 表示最后一行

last_value(sal) 的結(jié)果與 order by sal 排序有關(guān)。如果排序為order by sal desc, 則最終的結(jié)果為分組排序后sal的最小值(分組排序后的最后一個值), 當(dāng)deptno為10時，max_sal為1300。

2. 理解over()函數(shù)

2.1 兩個order by 的執(zhí)行機制

分析函數(shù)是在整個SQL查詢結(jié)束后(SQL語句中的order by 的執(zhí)行比較特殊)再進行的操作，也就是說SQL語句中的order by也會影響分析函數(shù)的執(zhí)行結(jié)果：

• 兩者一致：如果SQL語句中的order by 滿足分析函數(shù)分析時要求的排序，那么SQL語句中的排序?qū)⑾葓?zhí)行，分析函數(shù)在分析時就不必再排序。
• 兩者不一致：如果SQL語句中的order by 不滿足分析函數(shù)分析時要求的排序，那么SQL語句中的排序?qū)⒆詈笤诜治龊瘮?shù)分析結(jié)束后執(zhí)行排序。

2.2 分析函數(shù)中的分組、排序、窗口

分析函數(shù)包含三個分析子句：分組(partition by)、排序(order by)、窗口(rows)。

窗口就是分析函數(shù)分析時要處理的數(shù)據(jù)范圍，就拿sum來說，它是sum窗口中的記錄而不是整個分組中的記錄。因此我們在想得到某個欄位的累計值時，我們需要把窗口指定到該分組中的第一行數(shù)據(jù)到當(dāng)前行，如果你指定該窗口從該分組中的第一行到最后一行，那么該組中的每一個sum值都會一樣，即整個組的總和。

窗口子句中我們經(jīng)常用到指定第一行，當(dāng)前行，最后一行這樣的三個屬性：

• 第一行是 unbounded preceding
• 當(dāng)前行是 current row
• 最后一行是 unbounded following

窗口子句不能單獨出現(xiàn)，必須有order by 子句時才能出現(xiàn)，如：

LAST_VALUE(SAL) OVER (PARTITION BY DEPTNO ORDER BY SAL ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING )

以上示例指定窗口為整個分組.

而出現(xiàn)order by 子句的時候，不一定要有窗口子句，但效果會不一樣，此時窗口默認(rèn)是當(dāng)前組的第一行到當(dāng)前行！

SQL語句為：

SELECT DEPTNO, EMPNO, ENAME, SAL,last_value(SAL) OVER(PARTITION BY DEPTNO ORDER BY SAL) MAX_SAL FROM EMP;

等價于

SELECT DEPTNO, EMPNO, ENAME, SAL,last_value(SAL) OVER(PARTITION BY DEPTNO ORDER BY SAL ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) MAX_SAL FROM EMP;

結(jié)果如下圖所示：

當(dāng)省略窗口子句時：

• 如果存在order by, 則默認(rèn)的窗口是 unbounded preceding and current row.
• 如果同時省略order by, 則默認(rèn)的窗口是 unbounded preceding and unbounded following.

如果省略分組，則把全部記錄當(dāng)成一個組：

• 如果存在order by 則默認(rèn)窗口是unbounded preceding and current row
• 如果這時省略order by 則窗口默認(rèn)為 unbounded preceding and unbounded following

2.3 幫助理解over()的實例

例1：關(guān)注點：SQL無排序，over()排序子句省略

select deptno, empno, ename, sal, last_value(sal) over(partition by deptno) from emp;

例2：關(guān)注點：SQL無排序，over()排序子句有，窗口省略

select deptno, empno, ename, sal, last_value(sal) over(partition by deptno order by sal desc) from emp;

例3：關(guān)注點：SQL無排序，over()排序子句有，窗口也有，窗口特意強調(diào)全組數(shù)據(jù)

select deptno, empno, ename, sal, last_value(sal) over(partition by deptno order by sal rows between unbounded preceding and unbounded following) max_sal from emp;

例4：關(guān)注點：SQL有排序（正序），over() 排序子句無，先做SQL排序再進行分析函數(shù)運算

select deptno, mgr, ename, sal, hiredate, last_value(sal) over(partition by deptno)last_value from emp where deptno=30 order by deptno, mgr;

例5：關(guān)注點：SQL有排序（倒序），over() 排序子句無，先做SQL排序再進行分析函數(shù)運算

select deptno, mgr, ename, sal, hiredate, last_value(sal) over(partition by deptno)last_value from emp where deptno=30 order by deptno, mgr desc;

例6：關(guān)注點：SQL有排序（倒序），over()排序子句有，窗口子句無，此時的運算是：SQL先選數(shù)據(jù)但是不排序，而后排序子句先排序并進行分析函數(shù)處理（窗口默認(rèn)為第一行到當(dāng)前行），最后再進行SQL排序

select deptno, mgr, ename, sal, hiredate, min(sal) over(partition by deptno order by sal)last_value from emp where deptno=30 order by deptno, mgr desc;

select deptno, mgr, ename, sal, hiredate, min(sal) over(partition by deptno order by sal desc) last_value from emp where deptno=30 order by deptno, mgr desc;

3. 常見分析函數(shù)

3.1 演示表和數(shù)據(jù)的生成

建表語句：

create table t( BILL_MONTH VARCHAR2(12), AREA_CODE NUMBER, NET_TYPE VARCHAR(2), LOCAL_FARE NUMBER);

插入數(shù)據(jù)：

insert into t values("200405",5761,"G", 7393344.04);insert into t values("200405",5761,"J", 5667089.85);insert into t values("200405",5762,"G", 6315075.96);insert into t values("200405",5762,"J", 6328716.15);insert into t values("200405",5763,"G", 8861742.59);insert into t values("200405",5763,"J", 7788036.32);insert into t values("200405",5764,"G", 6028670.45);insert into t values("200405",5764,"J", 6459121.49);insert into t values("200405",5765,"G", 13156065.77);insert into t values("200405",5765,"J", 11901671.70);insert into t values("200406",5761,"G", 7614587.96);insert into t values("200406",5761,"J", 5704343.05);insert into t values("200406",5762,"G", 6556992.60);insert into t values("200406",5762,"J", 6238068.05);insert into t values("200406",5763,"G", 9130055.46);insert into t values("200406",5763,"J", 7990460.25);insert into t values("200406",5764,"G", 6387706.01);insert into t values("200406",5764,"J", 6907481.66);insert into t values("200406",5765,"G", 13562968.81);insert into t values("200406",5765,"J", 12495492.50);insert into t values("200407",5761,"G", 7987050.65);insert into t values("200407",5761,"J", 5723215.28);insert into t values("200407",5762,"G", 6833096.68);insert into t values("200407",5762,"J", 6391201.44);insert into t values("200407",5763,"G", 9410815.91);insert into t values("200407",5763,"J", 8076677.41);insert into t values("200407",5764,"G", 6456433.23);insert into t values("200407",5764,"J", 6987660.53);insert into t values("200407",5765,"G", 14000101.20);insert into t values("200407",5765,"J", 12301780.20);insert into t values("200408",5761,"G", 8085170.84);insert into t values("200408",5761,"J", 6050611.37);insert into t values("200408",5762,"G", 6854584.22);insert into t values("200408",5762,"J", 6521884.50);insert into t values("200408",5763,"G", 9468707.65);insert into t values("200408",5763,"J", 8460049.43);insert into t values("200408",5764,"G", 6587559.23);insert into t values("200408",5764,"J", 7342135.86);insert into t values("200408",5765,"G", 14450586.63);insert into t values("200408",5765,"J", 12680052.38);commit;

3.2 first_value()與last_value():求最值對應(yīng)的其他屬性

問題：取出每個月通話費最高和最低的兩個地區(qū)

思路：先進行g(shù)roup by bill_month, area_code使用聚合函數(shù)sum()求解出by bill_month, area_code的local_fare總和, 即sum(local_fare), 然后再運用分析函數(shù)進行求解每個月通話費用最高和最低的兩個地區(qū)。

select bill_month, area_code, sum(local_fare) local_fare,first_value(area_code) over(partition by bill_month order by sum(local_fare) desc rows between unbounded preceding and unbounded following) firstval,last_value(area_code) over(partition by bill_month order by sum(local_fare) desc rows between unbounded preceding and unbounded following) lastvalfrom t group by bill_month, area_code;

3.3 rank()、dense_rank()與row_number() 排序問題

演示數(shù)據(jù)再Oracle自帶的scott用戶下

1.rank()值相同時排名相同，其后排名跳躍不連續(xù)

select * from (select deptno, ename, sal,  rank() over(partition by deptno order by sal desc) rw from emp) where rw < 4;

2. dense_rank()值相同時排名相同，其后排名連續(xù)不跳躍

select * from (select deptno, ename, sal,  dense_rank() over(partition by deptno order by sal desc) rw from emp) where rw <= 4;

3. row_number()值相同時排名不相等，其后排名連續(xù)不跳躍

select * from (select deptno, ename, sal,  row_number() over(partition by deptno order by sal desc) rw from emp) where rw <= 4;

3.4 lag()與lead():求之前或之后的第N行

lag(arg1, arg2, arg3):

• arg1：是從其他行返回的表達式
• arg2：是希望檢索的當(dāng)前行分區(qū)的偏移量。是一個正的偏移量，是一個往回檢索以前的行數(shù)目
• arg3：是在arg2表示的數(shù)目超出了分組的范圍時返回的值

而lead()與lag()相反

select bill_month, area_code, local_fare cur_local_fare,lag(local_fare, 1, 0) over(partition by area_code order by bill_month)last_local_fare,lead(local_fare, 1, 0) over(partition by area_code order by bill_month) next_local_farefrom (select bill_month, area_code, sum(local_fare) local_fare from t group by bill_month, area_code);

3.5 rollup()與cube()：排列組合分組

group by rollup(A, B, C)：

首先會對 (A, B, C) 進行g(shù)roup by,

然后再對 (A, B) 進行g(shù)roup by,

其后再對 (A) 進行g(shù)roup by,

最后對全表進行匯總操作。

group by cube(A, B, C):

則首先會對 (A, B, C) 進行g(shù)roup by,

然后依次是 (A, B), (A, C), (A), (B, C), (B), (C),

最后對全表進行匯總操作。

1.生成演示數(shù)據(jù)：

create table scott.tt as select * from dba_indexes;

2.普通group by 體驗

select owner, index_type, status, count(*) from tt where owner like "SY%" group by owner, index_type, status;

3. group by rollup(A, B, C)：

首先會對 (A, B, C) 進行g(shù)roup by,

然后再對 (A, B) 進行g(shù)roup by,

其后再對 (A) 進行g(shù)roup by,

最后對全表進行匯總操作。

select owner, index_type, status, count(*) from tt where owner like "SY%" group by rollup(owner, index_type, status);

4. group by cube(A, B, C):

則首先會對 (A, B, C) 進行g(shù)roup by,

然后依次是 (A, B), (A, C), (A), (B, C), (B), (C),

最后對全表進行匯總操作。

select owner, index_type, status, count(*) from tt where owner like "SY%" group by cube(owner, index_type, status);

（只截取了部分圖）

3.6 max()、min()、sum()與avg()：求移動的最值、總和與平均值

問題：計算出各個地區(qū)連續(xù)3個月的通話費用的平均數(shù)(移動平均值)

select area_code, bill_month, local_fare,sum(local_fare) over(partition by area_code order by to_number(bill_month)     range between 1 preceding and 1 following) month3_sum,avg(local_fare) over(partition by area_code order by to_number(bill_month)     range between 1 preceding and 1 following) month3_avg,max(local_fare) over(partition by area_code order by to_number(bill_month)     range between 1 preceding and 1 following) month3_max,min(local_fare) over(partition by area_code order by to_number(bill_month)     range between 1 preceding and 1 following) month3_minfrom (select bill_month, area_code, sum(local_fare) local_fare from t   group by area_code, bill_month);

問題：求各地區(qū)按月份累加的通話費

select area_code, bill_month, local_fare, sum(local_fare) over(partition by area_code order by bill_month asc) last_sum_valuefrom(select area_code, bill_month, sum(local_fare) local_fare from t group by area_code, bill_month) order by area_code, bill_month;

3.7 ratio_to_report()：求百分比

問題：求各地區(qū)花費占各月花費的比例

select bill_month, area_code, sum(local_fare) local_fare,RATIO_TO_REPORT(sum(local_fare)) OVER (partition by bill_month) AS area_pctfrom t group by bill_month, area_code;

總結(jié)

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