SQL基础操作_6_处理数字

目录

​​7.7 处理数字​​

​​7.7.1 计算某列的最小/大值​​

​​7.7.2 计算某列的平均值​​

​​7.7.3 计算某列的总和​​

​​7.7.4 计算表的行数​​

​​7.7.5 非NULL值的列的个数​​

​​7.7.6 NULL值的列的个数​​

​​7.7.7 含NULL值的列的聚合​​

​​7.7.8 计算累加值​​

​​7.7.9 计算累加乘​​

​​7.7.10 计算累加差​​

​​7.7.11 计算某列重复最多的值​​

​​7.7.12 计算某列的中间值​​

​​7.7.13 计算组内总和的占比​​

​​7.7.14 计算组总和的占比​​

​​7.7.15 计算不含最大/小值的均值​​

​​7.7.16 计算标准差​​

7.7 处理数字

注:数据集和表结构见 ​​SQL基础操作_1_检索数据​​

7.7.1 计算某列的最小/大值

需求：按照部门编号分组找出EMP表中工资最低/最高值,同时返回出deptno

解决方法:通过聚合函数MIN/MAX结合GROUP BY来完成.

SQLServer、Mysql、Oracle:

SELECT DEPTNO,MIN(SAL) Min_SAL,MAX(SAL) Max_SAL
FROM emp
GROUP BY DEPTNO

执行结果:

延展阅读:

如果想计算出所有emp表里工资的最低和最高,则只需要取MIN和MAX即可,不加GROUP BY.

SELECT MIN(SAL) Min_SAL,MAX(SAL) Max_SAL
FROM emp

执行结果:

7.7.2 计算某列的平均值

需求：按照部门编号分组找出EMP表中工资平均值,同时返回出deptno

解决方法:通过聚合函数AVG结合GROUP BY来完成.

SQLServer、Mysql、Oracle:

SELECT DEPTNO,AVG(SAL) Avg_SAL
FROM emp
GROUP BY DEPTNO

执行结果:

7.7.3 计算某列的总和

需求：按照部门编号分组找出EMP表中工资总和,同时返回出deptno

解决方法:通过聚合函数SUN结合GROUP BY来完成.

SQLServer、Mysql、Oracle:

SELECT DEPTNO,SUM(SAL) Sum_SAL
FROM emp
GROUP BY DEPTNO

执行结果:

7.7.4 计算表的行数

需求: 计算EMP表的总行数.                

解决方法:通过COUNT(*)来完成.

SQLServer、Mysql、Oracle:

SELECT COUNT(*) AS rowCnt
FROM emp

执行结果:

7.7.5 非NULL值的列的个数

需求：取EMP表里COMM字段非空的个数.      

解决方法:通过COUNT(comm)来完成.

Sql Server、Mysql、Oracle：

SELECT COUNT(comm) AS Comm_Cnt FROM emp

执行结果:

7.7.6 NULL值的列的个数

需求：取EMP表里COMM字段为空的个数.      

解决方法:通过SUM CASEWHEN comm IS NULL … 来统计.

Sql Server、Mysql、Oracle：

SELECT SUM(CASE WHEN comm IS NULL THEN 1 ELSE 0 END) AS NULL_Num
FROM emp
WHERE comm IS NULL;

执行结果:

7.7.7 含NULL值的列的聚合

需求：验证行NULL的列的聚合函数的计算结果.

解决方法:通过MIN、MAX、SUM、AVG、COUNT(*)来完成.

Sql Server、Mysql、Oracle：

SELECT MIN(DATA) Min_Data,MAX(DATA) Max_Data,SUM(DATA) Sum_Data,AVG(DATA) Avg_Data,COUNT(*) AS Row_Cnt FROM
(
SELECT 1 AS DATA
   UNION ALL
SELECT NULL AS DATA
   UNION ALL
SELECT 3 AS DATA
   UNION ALL
SELECT NULL AS DATA
)A

执行结果:

由上面的结果可见,AVG时NULL值未参与运算.

7.7.8 计算累加值

需求：计算EMP表里SAL字段的累加值,这里按照SAL、EMPNO排序.

解决方法:通过SUM OVER()函数来完成.

Sql Server、Oracle：

SELECT sal,empno,SUM(sal)OVER(ORDER BY sal,empno) Accu_Num
FROM emp;

执行结果：

Sql Server、Oracle 、Mysql：

SELECT B.sal,B.empno,(SELECT SUM(A.sal) FROM emp A WHERE A.empno<=B.empno) AS Accu_Cnt
FROM emp B
ORDER BY Accu_Cnt

SELECT B.sal,B.empno,SUM(A.sal) AS Accu_Cnt
FROM emp B
JOIN emp A
    ON A.empno <=B.empno
GROUP BY B.sal,B.empno
ORDER BY Accu_Cnt

7.7.9 计算累加乘

需求：计算EMP表里SAL字段的累计乘积值,这里按照SAL、EMPNO排序.

解决方法:通过SUM OVER()EXP LOG LN函数来完成.

Sql Server：

SELECT sal,empno,LOG(sal) AS Log_Sal,EXP(SUM(LOG(sal))OVER(ORDER BY sal,empno)) Accu_Prod
FROM emp;

执行结果:

Oracle：

SELECT sal,empno,LN(sal) AS Log_Sal,EXP(SUM(LN(sal))OVER(ORDER BY sal,empno)) Accu_Prod
FROM emp;

Mysql:

SELECT B.sal,B.empno,(SELECT exp(SUM(ln(A.sal))) FROM emp A WHERE A.empno<=B.empno) AS Accu_Cnt
FROM emp B
ORDER BY Accu_Cnt

SELECT B.sal,B.empno,exp(SUM(ln(A.sal))) AS Accu_Cnt
FROM emp B
JOIN emp A
    ON A.empno <=B.empno
GROUP BY B.sal,B.empno
ORDER BY Accu_Cnt

7.7.10 计算累加差

需求：计算EMP表里SAL字段的累计乘积值,这里按照SAL、EMPNO排序.

解决方法:通过SUM OVER()函数来完成,这里SAL要取反,即SAL的负数.

Sql Server、Oracle:

SELECT deptno,sal,empno,SUM(CASE WHEN RN=1 THEN SAL ELSE -sal END)OVER(PARTITION BY deptno ORDER BY sal,empno) Accu_Diff FROM
(
SELECT deptno,sal,empno,ROW_NUMBER()OVER(PARTITION BY deptno ORDER BY sal,empno)RN
FROM emp
)A

执行结果:

Mysql:

暂未实现.

7.7.11 计算某列重复最多的值

需求：计算EMP表里SAL字段重复最多的值,以部门编号为20的为例.

解决方法:通过窗口函数或则借助聚合函数来完成.

Sql Server、Mysql:

SELECT sal FROM emp WHERE deptno=20
GROUP BY sal HAVING COUNT(*) >=
ALL (SELECT COUNT(*) FROM emp WHERE deptno =20 GROUP BY SAL)

-- 或者将ALL换成MAX
SELECT sal FROM emp WHERE deptno=20
GROUP BY sal HAVING COUNT(*) >=
(SELECT MAX(RN) FROM
    (SELECT COUNT(*) AS RN FROM emp WHERE deptno =20 GROUP BY SAL)A
)

Oracle：

7.7.12 计算某列的中间值

需求：计算EMP表按照deptno分组，找出排在中间的SAL

解决方法:通过窗口函数集合COUNT（*）通过序号取模来判断.

SQL Server：

SELECT B.deptno,A.sal middle_Sal,B.row_CN,CASE WHEN (B.row_CN%2=0) THEN B.row_CN/2 ELSE (row_CN+1)/2 END Middle FROM
(
SELECT empno,sal,deptno,ROW_NUMBER()OVER(PARTITION BY deptno ORDER BY sal) AS RN FROM emp
 )A
JOIN
   (
   SELECT deptno,COUNT(*) AS row_CN FROM emp
   GROUP BY deptno
   )B
ON A.deptno = B.deptno
AND A.RN = CASE WHEN (B.row_CN%2=0) THEN B.row_CN/2 ELSE (row_CN+1)/2 END

执行结果：

同理我们可以在mysql实现：

SELECT B.deptno,A.SAL,B.row_CN,ROUND(CASE WHEN (B.row_CN%2=0) THEN B.row_CN/2 ELSE (row_CN+1)/2 END) AS Middle
FROM
(
SELECT heyf_tmp.deptno,heyf_tmp.empno,heyf_tmp.sal,@rownum :=@rownum+1AS rn ,
        IF(@pdept= heyf_tmp.deptno,@rank:=@rank+1, @rank:=1) AS rank,
        @pdept:=heyf_tmp.deptno AS pre_deptno
        FROM ( 
        SELECT A.deptno,A.sal,A.empno FROM emp A
        ORDER BY deptno,sal
        ) heyf_tmp ,
        (SELECT @rownum :=0 , @pdept :=NULL ,@rank :=0) a
)A
JOIN
(
SELECT deptno,COUNT(*) AS row_CN FROM emp
   GROUP BY deptno
) B
ON A.deptno = B.deptno AND A.RANK =CASE WHEN (B.row_CN%2=0) THEN B.row_CN/2 ELSE (row_CN+1)/2 END

执行结果：

7.7.13 计算组内总和的占比

需求：计算EMP表按照deptno分组，计算SAL在每组总和中的占比

解决方法:通过每行的SAL除以每组的SUM（SAL）来实现.

SQL Server：

SELECT A.deptno,SAL,CAST(ROUND(SAL/sum_num,2) AS DECIMAL(10, 2)) AS percent FROM
emp A
JOIN
(
SELECT deptno,SUM(SAL) AS sum_num
FROM emp
GROUP BY deptno
)B
ON A.deptno = B.deptno

执行结果：

Mysql：

SELECT A.deptno,SAL,ROUND(SAL/sum_num,2) AS percent FROM
emp A
JOIN
(
SELECT deptno,SUM(SAL) AS sum_num
FROM emp
GROUP BY deptno
)B
ON A.deptno = B.deptno

7.7.14 计算组总和的占比

需求：计算EMP表按照deptno分组，计算每组的SAL总和与所以记录总和中的占比

解决方法:通过每组SUM（SAL）窗口函数再除以记录总和来实现.

Sql Server、Oracle：

SELECT DISTINCT deptno,SUM(SAL)OVER(PARTITION BY deptno) AS sum_num,SUM(SAL) OVER() AS sum_total,
CAST(ROUND(SUM(SAL)OVER(PARTITION BY deptno)/SUM(SAL)OVER(),2)AS DECIMAL(10, 2)) AS group_percent
FROM emp

执行结果：

Sql Server：

SELECT deptno,CAST(SUM(SAL)/(SELECT SUM(SAL) FROM EMP)AS DECIMAL(10, 2)) AS group_percent
FROM EMP
GROUP BY deptno

Mysql：

SELECT deptno,ROUND(SUM(SAL)/(SELECT SUM(SAL) FROM EMP), 2) AS group_percent
FROM EMP
GROUP BY deptno

执行结果:

7.7.15 计算不含最大/小值的均值

需求：计算EMP表按照deptno分组，计算每组的SAL均值,这里不包含最大和最小值.

解决方法:通过每组踢除最大/小值再AVG的方式来实现.

Sql Server、Mysql、Oracle:

SELECT A.deptno,AVG(A.SAL) AS avg_SAL
FROM EMP A
LEFT JOIN
(
SELECT deptno,MIN(SAL) AS SAL FROM EMP
   GROUP BY deptno 
UNION
   SELECT deptno,MAX(SAL) AS SAL FROM EMP
   GROUP BY deptno
)B
ON A.deptno = B.deptno AND A.SAL = B.SAL
WHERE B.deptno IS NULL
GROUP BY A.deptno

执行结果:

7.7.16 计算标准差

需求：计算EMP表按照deptno分组，计算每组的SAL的标准差.

解决方法:通过每组踢出最大/小值再AVG的方式来实现.

SQL Server:

SELECT DEPTNO,STDEVP(SAL) AS Stdevp_Value FROMEMP
GROUP BY DEPTNO

执行结果:

注:

1)  标准差的公式见下:

2) STDEVP和STDEV的区别是STDEVP除以的是N,而STDEV除以的是N-1

Mysql:

SELECT A.DEPTNO,SQRT(SUM(POWER((A.SAL-avg_SAL),2))/cnt) Stdevp_Value FROM EMP A
JOIN
(
SELECT DEPTNO,AVG(SAL) AS avg_SAL,COUNT(*) AS cnt FROM EMP
GROUP BY DEPTNO
)B
ON A.deptno = B.deptno
GROUP BY A.deptno

结果同上.