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法律研究如何在 Oracle 中识别层次结构表中不是任何其他行的父行的行？
问题陈述：如何在层次结构表中识别叶子行，即不是任何其他行的父行的行。
解决方案：Oracle 提供 CONNECT_BY_ISLEAF 子句来识别不是任何其他行的父行的行。首先让我们看看 connect_by_isleaf 是如何工作的。
SQL
/*
Function - Example to show if the row is parent of any other rows or not
Tables Used - students Data - Documented below
*/
SELECT student_id,
level,
CASE WHEN connect_by_isleaf = 0
THEN 'Yes'
ELSE 'No'
END AS is_parent,
lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name
FROM students
START WITH professor_id IS null
CONNECT BY PRIOR student_id = professor_id;输出：上面 SQL 的几行
100 1 Yes SMITH JAMES 101 2 Yes -JOHNSON JOHN 108 3 Yes -RODRIGUEZ JOSEPH 109 4 No -WILSON THOMAS 110 4 No -MARTINEZ CHRISTOPHER 111 4 No -ANDERSON DANIEL 112 4 No -TAYLOR PAUL 113 4 No -THOMAS MARK 102 2 Yes -WILLIAMS ROBERT 103 3 Yes -BROWN MICHAEL 104 4 No -JONES WILLIAM 105 4 No -MILLER DAVID
在上面的 SQL 中，connect_by_isleaf 的值 0 表示该行是父行并具有更多子行，而值 1 表示叶子节点/记录，它不是任何其他行的父行。
connect_by_isleaf 的一个有趣的实现是识别不是教授/管理员的学生。以下 SQL 将显示如何实现它。
SQL
/* Function - Example to identify students that are not professors/adminstrators Tables Used - students Data - Documented below */ SELECT student_id,first_name || ' ' || last_name AS student_name, connect_by_root first_name || ' ' || last_name AS manager_name FROM students WHERE connect_by_isleaf = 1 START WITH professor_id IS null CONNECT BY PRIOR student_id = professor_id;
输出：上面 SQL 的几行
109 WILSON THOMAS SMITH THOMAS 110 MARTINEZ CHRISTOPHER SMITH CHRISTOPHER 111 ANDERSON DANIEL SMITH DANIEL 112 TAYLOR PAUL SMITH PAUL 113 THOMAS MARK SMITH MARK 104 JONES WILLIAM SMITH WILLIAM 105 MILLER DAVID SMITH DAVID 106 DAVIS RICHARD SMITH RICHARD 107 GARCIA CHARLES SMITH CHARLES
数据准备：用于该问题的数据如下所示。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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