如何在 Oracle 中使用 Grouping 子句处理 NULL 值？

问题

您希望将 GROUPING() 与 ROLLUP、CUBE 和 SETS 函数一起使用。

解决方案

GROUPING() 函数接受一个列并返回 0 或 1。当列值为 null 时，此函数返回 1；当列值为非 null 时，返回 0。但是，GROUPING() 仅在使用 ROLLUP 或 CUBE 的查询中使用。当您希望在返回 null 的情况下显示一个值时，GROUPING() 非常有用。

ROLLUP 中的单列 GROUPING()

将列传递给 ROLLUP 的 SQL

以下示例中的最后一行将生成费用总计/总和。此总数表示为 NULL。

示例

SELECT class_id, SUM(fees)
   FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

输出

最后一行中的 class_id 列为 null。我们可以使用 GROUPING() 函数来确定此列是否为 null，如下面的查询所示。

对于具有非 null class_id 值的行，GROUPING() 返回 0；对于具有 null class_id 的最后一行，返回 1。

示例

SELECT  GROUPING(class_id) As grp, class_id, SUM(fees)
FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

输出

现在我们将使用 CASE 语句来设置有意义的值。

示例

SELECT
   CASE GROUPING(class_id)
      WHEN 1 THEN 'Total fees'
      ELSE class_id
  END AS class_group,
  SUM(fees) AS total
FROM students
GROUP BY ROLLUP(class_id)
ORDER BY class_id;

输出

CUBE 中的 GROUPING()

示例

SELECT
  CASE GROUPING(class_id)
    WHEN 1 THEN 'Total Salaries'
    ELSE class_id
  END AS job_group,
  SUM(fees) AS total_fees
FROM students
GROUP BY CUBE(class_id)
ORDER BY class_id;

输出

GROUPING SETS 子句通常比 CUBE 提供更好的性能。因此，您应尽可能将 GROUPING SETS 作为首选选项，而不是 CUBE。

GROUPING SETS 子句

示例

SELECT department_id, class_id, SUM(fees) AS total_fees
FROM students
GROUP BY GROUPING SETS(department_id, class_id)
ORDER BY department_id, class_id;

输出

数据准备：用于问题的數據如下所示。数据完全是为了演示目的而编造的。

示例

DROP TABLE students;
COMMIT;

CREATE TABLE students
    ( student_id    NUMBER(6)
    , first_name     VARCHAR2(20)
    , last_name      VARCHAR2(25) CONSTRAINT  stu_last_name_nn  NOT NULL
    , email          VARCHAR2(40) CONSTRAINT  stu_email_nn  NOT NULL
    , phone_number   VARCHAR2(20)
      , join_date      DATE CONSTRAINT           stu_join_date_nn  NOT NULL
    , class_id         VARCHAR2(20) CONSTRAINT stu_job_nn  NOT NULL
    , fees           NUMBER(8,2)
    , professor_id     NUMBER(6)
    , department_id  NUMBER(4)
    , CONSTRAINT     stu_fees_min CHECK (fees > 0)
    , CONSTRAINT     stu_email UNIQUE (email)
    ) ;

示例

CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','[email protected]','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','[email protected]','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','[email protected]','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','[email protected]','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','[email protected]','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','[email protected]','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','[email protected]','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','[email protected]','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','[email protected]','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','[email protected]','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','[email protected]','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','[email protected]','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','[email protected]','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','[email protected]','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);

COMMIT;

Kiran P

更新于： 2020-12-05

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