最近在研究Oracle PLSQL中对于XML的系列操作。结合工作中使用的知识和参考资料整理出以下相关内容：
一 如何生成XML文件：
1、使用dbms_xmlquery和utl_file内置包（scott用户执行）
CREATE OR REPLACE DIRECTORY xml_dir AS 'd:appxml';
DROP SEQUENCE seq_filename;
CREATE SEQUENCE seq_filename
MINVALUE 10000
MAXVALUE 99999
INCREMENT BY 1
START WITH 10000
NOCYCLE;
DECLARE
v_filename Varchar2(50) := 'Empmsg'||to_char(seq_filename.nextval)||'.xml';
xml_str clob;
xml_file utl_file.file_type;
offset number;
buffer varchar2(32767);
buffer_size number;
BEGIN
offset := 1;
buffer_size := 3000;
xml_file := utl_file.fopen('XML_DIR', v_filename, 'w');
xml_str := dbms_xmlquery.getxml('select empno,
ename,
job,
mgr,
hiredate,
sal,
comm,
deptno
from emp');
while (offset < dbms_lob.getlength(xml_str)) loop
buffer := dbms_lob.substr(xml_str, buffer_size, offset);
utl_file.put(xml_file, buffer);
utl_file.fflush(xml_file);
offset := offset + buffer_size;
end loop;
utl_file.fclose(xml_file);
END;
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2、使用XMLELEMENT系列内置函数返回xml（sys用户执行）
DECLARE
v_filename Varchar2(50) := 'Empmsg'||to_char(scott.seq_filename.nextval)||'.xml';
xml_str clob;
xml_file utl_file.file_type;
offset number;
buffer varchar2(32767);
buffer_size number;
BEGIN
offset := 1;
buffer_size := 3000;
xml_file := utl_file.fopen('XML_DIR', v_filename, 'w');
SELECT XMLElement("DEPARTMENT"
, XMLAttributes( department_id as "ID"
, department_name as "NAME"
)
, XMLElement("EMPLOYEES"
, (SELECT XMLAgg( XMLElement("EMPLOYEE"
, XMLForest(employee_id as "ID"
,first_name||' '||last_name as "NAME"
)
)
)
FROM hr.employees emp
WHERE emp.department_id = dept.department_id
)
)
).getclobval() INTO xml_str
FROM hr.departments dept
WHERE department_id = 20;
while (offset < dbms_lob.getlength(xml_str)) loop
buffer := dbms_lob.substr(xml_str, buffer_size, offset);
utl_file.put(xml_file, buffer);
utl_file.fflush(xml_file);
offset := offset + buffer_size;
end loop;
utl_file.fclose(xml_file);
END;
--XMLElement: 将一个关系值转换为XML元素的函数，格式为值
--XMLAttributes: 用于在SQL查询返回的 XML 元素中设置属性的函数
--XMLForest: 该函数返回一个或多个子元素的集合,该函数使用列名做为XML元素的名称并用SQL值表达式做为XML元素的内容，但使用时不能指定元素的属性
--XMLAgg: 在GROUP BY查询中对XML数据进行分组或汇总的函数
PS: 使用SPOOL方式导出文件：
SET TRIMSPOOL ON
SET TERMOUT ON
SET FEEDBACK OFF
SET VERIFY OFF
SET ECHO OFF
SET PAGESIZE 999
SET HEAD OFF
SET HEADING OFF
SET LONG 5000
spool c:a.xml
SELECT XMLElement("DEPARTMENT"
, XMLAttributes( department_id as "ID"
, department_name as "NAME"
)
, XMLElement("EMPLOYEES"
, (SELECT XMLAgg( XMLElement("EMPLOYEE"
, XMLForest(employee_id as "ID"
,first_name||' '||last_name as "NAME"
)
)
)
FROM employees emp
WHERE emp.department_id = dept.department_id
)
)
) a
FROM departments dept
WHERE department_id = 10;
spool off
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