如何生成带有嵌套值的XML？
问题陈述：
您想生成一个复杂的XML文档，其中的嵌套值位于不同的级别。
解决方案：Oracle具有许多用于从常规数据生成XML的功能和过程。为了演示用法，我将使用studentdata。我们将假设我们想将学生的学生ID用作根元素的XML属性，并添加有关费用的详细信息，将付款期限指定为属性，并添加货币详细信息。
Oracle函数XMLROOT，XMLELEMENT和XMLATTRIBUTE提供了对所需XML结构的完全控制。
XMLROOT提供必要的XML标头，以将我们的结果从XML片段转换为完整的XML文档。使用XMLROOT时导致
<?xml version="1.0"?>
XMLELEMENT的工作原理与dbms_output.put_line和连接命令几乎相同。XMLELEMENT将源列与提供的元素名称一起输出，以形成结果的XML构建块。您可以根据需要将对XMLELEMENT的调用串在一起（就像您可以连接任意数量的字符串一样），并且对其进行操作的表达式本身可以是对XMLELEMENT的另一个调用。
XMLATTRIBUTES指示Oracle将给定的列或表达式作为由XMLELEMENT的父调用创建的元素的属性。
XMLAttributes（student_id为“student_id”）
SQL：生成嵌套的XML
SELECT XMLRoot(
XMLElement("student",
XMLAttributes(student_id as "student_id"),
XMLElement("FirstName", first_name),
XMLElement("LastName", last_name),
XMLElement("fees",
XMLAttributes('yearly' as "Period"),
XMLElement("Amount", fees),
XMLElement("Currency", 'USD'))
),
VERSION '1.0') student_XML
FROM students ;输出结果
<?xml version="1.0"?>
<student student_id="100">
<FirstName>SMITH</FirstName>
<LastName>JAMES</LastName>
<fees Period="yearly">
<Amount>24000</Amount>
<Currency>USD</Currency>
</fees>
</student>数据准备：用于该问题的数据如下所示。数据完全用于演示目的。
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;