oracle中xml遇到单行子查询返回多行答案

【问题标题】：xml in oracle encounter single-row subquery returns more than one roworacle中xml遇到单行子查询返回多行
【发布时间】：2013-05-25 17:25:02
【问题描述】：

这是我用于创建表和插入 xml 列的代码。

--删除架构

BEGIN
DBMS_XMLSCHEMA.DELETESCHEMA(
   'http://xmlns.oracle.com/xdb/schemas/HZHE18/handBook',
   dbms_xmlschema.DELETE_CASCADE_FORCE);
END;

--注册二进制模式

BEGIN
DBMS_XMLSCHEMA.REGISTERSCHEMA(SCHEMAURL => 'handBook',
schemadoc => '<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">

<xs:annotation>
    <xs:documentation> Author: Andy(Haichuan) Zheng Schema for Web Handbook data
    </xs:documentation>
</xs:annotation>

<xs:simpleType name="code-style">
    <xs:restriction base="xs:string">
        <xs:pattern value="[A-Z][A-Z][A-Z][0-9][0-9][0-9][0-9]"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="level-style">
    <xs:restriction base="xs:string">
        <xs:enumeration value="Undergraduate"/>
        <xs:enumeration value="Postgraduate"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="email-style">
    <xs:restriction base="xs:string">
        <xs:pattern value="[^@]+@[^\.]+\..+"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="point_lvl_type">
    <xs:restriction base="xs:positiveInteger">
        <xs:enumeration value="3"/>
        <xs:enumeration value="6"/>
        <xs:enumeration value="12"/>
        <xs:enumeration value="24"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="offered_type">
    <xs:restriction base="xs:string">
        <xs:enumeration value="First semester"/>
        <xs:enumeration value="Second semester"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="mode_type">
    <xs:restriction base="xs:string">
        <xs:enumeration value="Day"/>
        <xs:enumeration value="Evening"/>
        <xs:enumeration value="Off-campus"/>
    </xs:restriction>
</xs:simpleType>

<xs:simpleType name="campus_type">
    <xs:restriction base="xs:string">
        <xs:enumeration value="Caulfield"/>
        <xs:enumeration value="Gippsland"/>
        <xs:enumeration value="Sunway"/>
        <xs:enumeration value="Clayton"/>
        <xs:enumeration value="South Africa"/>
    </xs:restriction>
</xs:simpleType>

<xs:element name="handbook">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="page_info" minOccurs="1" maxOccurs="unbounded"/>
            <xs:element ref="unit" minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

<xs:element name="page_info">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="sub_date" type="xs:date"/>
        </xs:sequence>
        <xs:attribute name="author" type="xs:string"/>
    </xs:complexType>
</xs:element>

<xs:element name="unit">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="u_name" type="xs:string"/>
            <xs:element name="level" type="level-style"/>
            <xs:element ref="chief_examiner"/>
            <xs:element name="point_lvl" type="point_lvl_type"/>
            <xs:element name="prerequisites" type="code-style" maxOccurs="unbounded"
                minOccurs="0"/>
            <xs:element name="prohibitions" type="code-style" maxOccurs="unbounded"
                minOccurs="0"/>
            <xs:element ref="availability"/>
            <xs:element name="synopsis" type="xs:string"/>
            <xs:element name="assessment" type="xs:string"/>
            <xs:element name="contact_hours" type="xs:string"/>
        </xs:sequence>
        <xs:attribute name="code" type="code-style"/>
    </xs:complexType>
</xs:element>

<xs:element name="chief_examiner">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="name" type="xs:string"/>
            <xs:element name="email" type="email-style"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

<xs:element name="availability">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="offered" type="offered_type" maxOccurs="unbounded"/>
            <xs:element name="mode" type="mode_type" maxOccurs="unbounded"/>
            <xs:element name="campus" type="campus_type" maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

</xs:schema>',
LOCAL => TRUE,
GENTYPES => FALSE,
GENTABLES => FALSE,
FORCE => FALSE,
options => DBMS_XMLSCHEMA.REGISTER_BINARYXML);
end;

--丢弃并清理回收站

drop table units_handbook purge;

PURGE RECYCLEBIN;

--创建表 CREATE TABLE units_handbook ( unit_code varchar2(7) 主键， XML_detail XMLTYPE NOT NULL) XMLTYPE COLUMN XML_detail 存储为二进制 XML XMLSCHEMA "http://xmlns.oracle.com/xdb/schemas/HZHE18/handBook" ELEMENT《手册》；

-- 填充表格

insert into units_handbook values('FIT2077', 
'<handbook>
    <page_info author = "Haichuan Zheng">
        <sub_date>2013-05-28</sub_date>
    </page_info>
    <unit code="FIT2077">
        <u_name>Advanced Data Management</u_name>
        <level>Undergraduate</level>
        <chief_examiner>
             <name>Mr Lindsay Smith</name>
             <email>Lindsay.Smith@monash.edu</email>
        </chief_examiner>
        <point_lvl>6</point_lvl>
        <prerequisites>FIT1004</prerequisites>
       <prerequisites>CSE2132</prerequisites>
    <prohibitions>CSE3000</prohibitions>
        <prohibitions>FIT3118</prohibitions>
    <prohibitions>FIT4038</prohibitions>
    <availability>
        <offered>First semester</offered>
        <mode>Day</mode>
        <campus>Caulfield</campus>
    </availability>
    <synopsis><![CDATA[This unit extends the study from FIT1004 Data management. 
        FIT2077 will introduce more advanced concepts in the areas of database design, SQL, 
        query optimisation and the handling of unstructured data (XML) both externally
        and within a database. The issue of "Big Data" and the role played by BI technologies 
        and data warehouses will be explored.]]></synopsis>
    <assessment>Examination (3 hours): 60%; In-semester assessment: 40%</assessment>
    <contact_hours>2 hrs lectures/wk, 2 hrs laboratories/wk</contact_hours>
</unit>
</handbook>');

insert into units_handbook values('FIT4038', 
'<handbook>
<page_info author = "Haichuan Zheng">
    <sub_date>2013-05-28</sub_date>
</page_info>
<unit code="FIT4038">
    <u_name>Database management and implementation</u_name>
    <level>Postgraduate</level>
    <chief_examiner>
        <name>Associate Professor David Taniar</name>
        <email>David.Taniar@monash.edu</email>
    </chief_examiner>
    <point_lvl>6</point_lvl>
    <prerequisites>FIT9019</prerequisites>
    <prerequisites>FIT9003</prerequisites>
    <prohibitions>FIT3118</prohibitions>
    <prohibitions>CSE3000</prohibitions>
    <availability>
        <offered>First semester</offered>
        <mode>Day</mode>
        <campus>Caulfield</campus>
    </availability>
    <synopsis><![CDATA[This unit looks at the design and implementation issues of 
        database management systems. Advanced database design using the object-relational approach 
        and multi-dimensional database design are explored. Record, file 
        and index structures are dealt with at the basic level. 
        Higher level details of consistency, atomicity and durability are
        introduced along with modern trends in databases.]]></synopsis>
    <assessment>Examination (3 hours): 60%; In-semester assessment: 40%</assessment>
    <contact_hours>2 hrs lectures/wk, 2 hrs laboratories/wk</contact_hours>
</unit>
</handbook>');

我的问题是，当我想以 xml 格式检索所有 u_name 时，我收到此错误消息 ORA-01427: single-row subquery returns more than one row

这是我的代码

  select xmlelement("unit",xmlelement("u_name",
  (
   SELECT
      EXTRACTVALUE(u.XML_detail, '/handbook/unit/u_name')
    FROM
       units_handbook u
 )
  ) )
  from units_handbook;

【问题讨论】：

标签： sql xml oracle

【解决方案1】：

这是因为您的内部查询返回不止一行（因为它在整个表上运行）。

你为什么不能这样做：

select xmlelement("unit",xmlelement("u_name",EXTRACTVALUE(u.XML_detail, '/handbook/unit/u_name')
    ))
  from units_handbook u;

如果您必须在内部查询中（在 select 子句中）使用它，那么您需要以某种方式连接记录或确保您只有一行。
作为

select xmlelement("unit",xmlelement("u_name",
  (
   SELECT
      EXTRACTVALUE(u.XML_detail, '/handbook/unit/u_name')
    FROM
       units_handbook u
    WHERE u.id = ou.id
 )
  ) )
  from units_handbook ou;

Here is a sqlfiddle demo

【讨论】：