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法学如何在 Oracle 数据库的层次数据中删除一个分支？
问题陈述：你需要自顶向下遍历层次数据，但不想在输出中包含特定分支。
解决方案：我们将研究此问题陈述的几个示例。
Oracle 提供 CONNECT BY 子句来指定层次查询，即如何连接父节点和子节点，以及 PRIOR 运算符来定义父节点之间的连接条件，以及 LEVEL 伪列来指示当前行距离根/父行的距离。
此外，我们可以使用 START WITH 子句来指示树导航的起始位置。我们必须使用 PRIOR 运算符来指定父行中与子行中的链接列具有相同值的列。
为了遍历整个层次结构，请移除 START WITH 子句。这将获取所有学生及其经理、经理的经理等等，直到顶级经理/主管。
在这个例子中，我将使用学生数据来演示问题的解决方案。
示例
SELECT student_id, first_name, last_name FROM students ;
输出
100 SMITH JAMES 101 JOHNSON JOHN 102 WILLIAMS ROBERT 103 BROWN MICHAEL 104 JONES WILLIAM 105 MILLER DAVID
假设你不想在这个报告中看到“BROWN MICHAEL”及其下属，这意味着我们需要从树中删除/修剪整个分支。为此，我们必须在 CONNECT BY 子句中将要删除的分支的顶部作为附加条件过滤掉，如下所示。
SQL
/*
Function - Remove the branch - "BROWN MICHAEL" from the output
Tables Used - students
Data - Documented below
*/
SELECT student_id,
level,
lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name
FROM students
START WITH professor_id IS null
CONNECT BY professor_id = PRIOR student_id
AND NOT (first_name || ' ' || last_name = 'BROWN MICHAEL' )
ORDER SIBLINGS by first_name, last_name;输出
100 1 SMITH JAMES 101 2 -JOHNSON JOHN 108 3 -RODRIGUEZ JOSEPH 111 4 -ANDERSON DANIEL 110 4 -MARTINEZ CHRISTOPHER 112 4 -TAYLOR PAUL 113 4 -THOMAS MARK 109 4 -WILSON THOMAS 102 2 -WILLIAMS ROBERT
如果我们只想忽略父节点，但仍然包含子节点，即排除“BROWN MICHAEL”，但仍然包含其下属学生，则过滤器应该位于 WHERE 子句中，如下所示
SQL
/*
Function - Remove only the branch head - BROWN MICHAEL from the output
Tables Used - students
Data - Documented below
*/
SELECT student_id,
level,
lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name
FROM students
WHERE NOT (first_name || ' ' || last_name = 'BROWN MICHAEL' )
START WITH professor_id IS null
CONNECT BY professor_id = PRIOR student_id
ORDER SIBLINGS by first_name, last_name;输出
100 1 SMITH JAMES 101 2 -JOHNSON JOHN 108 3 -RODRIGUEZ JOSEPH 111 4 -ANDERSON DANIEL 110 4 -MARTINEZ CHRISTOPHER 112 4 -TAYLOR PAUL 113 4 -THOMAS MARK 109 4 -WILSON THOMAS 102 2 -WILLIAMS ROBERT 106 4 -DAVIS RICHARD 107 4 -GARCIA CHARLES 104 4 -JONES WILLIAM
数据准备：用于问题的示例数据如下所示。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) , email VARCHAR2(40) , phone_number VARCHAR2(20) , join_date DATE , class_id VARCHAR2(20) , fees NUMBER(8,2) , professor_id NUMBER(6) , department_id NUMBER(4) ) ;
示例
CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','SMITH.JAMES@notreal.com','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','JOHNSON.JOHN@notreal.com','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','WILLIAMS.ROBERT@notreal.com','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','BROWN.MICHAEL@notreal.com','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','JONES.WILLIAM@notreal.com','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','MILLER.DAVID@notreal.com','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','DAVIS.RICHARD@notreal.com','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','GARCIA.CHARLES@notreal.com','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','RODRIGUEZ.JOSEPH@notreal.com','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','WILSON.THOMAS@notreal.com','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','MARTINEZ.CHRISTOPHER@notreal.com','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','ANDERSON.DANIEL@notreal.com','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','TAYLOR.PAUL@notreal.com','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','THOMAS.MARK@notreal.com','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);
COMMIT;
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