使用条件语句将'xml'节点动态导入sql server

Question

这与这个问题有关： Import 'xml' into Sql Server

您将如何处理可选的 XML 节点，假设“IsFixed”是一个可选节点，它存在于一个文件中而在另一个文件中不存在，如何在代码中放入条件以不执行“ Events.value" 并避免出现 Null 列？

DECLARE @XML XML = '
<EventSchedule>
    <Event Uid="2" Type="Main Event">
        <EventKind>MainEvent</EventKind>
        <Fields>
            <Parameter Name="Type" Value="TV_Show"/>
            <Parameter Name="Name" Value="The Muppets"/>
            <Parameter Name="Duration" Value="00:30:00"/>
        </Fields>
    </Event>
    <Event Uid="3" Type="Secondary Event">
        <EventKind>SecondaryEvent</EventKind>
        <Fields>
            <Parameter Name="Type" Value="TV_Show"/>
            <Parameter Name="Name" Value="The Muppets II"/>
            <Parameter Name="Duration" Value="00:30:00"/>
        </Fields>
    </Event>
</EventSchedule>'

如果 IsFixed 节点不存在，则不要执行粗线：

SELECT
    EventUID = Events.value('@Uid', 'int'),
    EventType = Events.value('@Type', 'varchar(20)'),
    ***EventIsFixed = Events.value('(IsFixed)[1]', 'varchar(20)'),***
    EventKind = Events.value('(EventKind)[1]', 'varchar(20)'),
    ParameterType = Events.value('(Fields/Parameter[@Name="Type"]/@Value)[1]', 'varchar(20)'),
    ParameterName = Events.value('(Fields/Parameter[@Name="Name"]/@Value)[1]', 'varchar(20)'),
    ParameterDuration = Events.value('(Fields/Parameter[@Name="Duration"]/@Value)[1]', 'varchar(20)')
FROM
    @XML.nodes('/EventSchedule/Event') AS XTbl(Events)

我尝试在 SELECT 语句中使用 CASE WHEN 但没有成功：

SELECT
    EventUID = Events.value('@Uid', 'int'),
    EventType = Events.value('@Type', 'varchar(20)'),
    CASE 
        WHEN Events.value('(IsFixed)[1]', 'varchar(20)') IS NOT NULL
        THEN ''
    END AS EventIsFixed,
    EventKind = Events.value('(EventKind)[1]', 'varchar(20)'),
    ParameterType = Events.value('(Fields/Parameter[@Name="Type"]/@Value)[1]', 'varchar(20)'),
    ParameterName = Events.value('(Fields/Parameter[@Name="Name"]/@Value)[1]', 'varchar(20)'),
    ParameterDuration = Events.value('(Fields/Parameter[@Name="Duration"]/@Value)[1]', 'varchar(20)')
FROM
    @XML.nodes('/EventSchedule/Event') AS XTbl(Events)

上面的代码仍然创建了一个作为 EventIsFixed 的空值列（输出表）。

EventUID    EventType   EventIsFixed    EventKind   ParameterType   ParameterName   ParameterDuration
2           Main Event                  MainEvent      TV_Show      The Muppets     00:30:00
3           Secondary Event             SecondaryEvent  TV_Show     The Muppets II  00:30:00

我想要做的是当 XML 节点存在时在表中有列，而当 XML 节点不存在时（动态地）根本没有列，如何？

Answer 1

使用exist()检查IsFixed是否存在。

IF @XML.exist('/EventSchedule/Event/IsFixed') = 1
BEGIN
  SELECT
      EventUID = Events.value('@Uid', 'int'),
      EventType = Events.value('@Type', 'varchar(20)'),
      EventIsFixed = Events.value('(IsFixed)[1]', 'varchar(20)'),
      EventKind = Events.value('(EventKind)[1]', 'varchar(20)'),
      ParameterType = Events.value('(Fields/Parameter[@Name="Type"]/@Value)[1]', 'varchar(20)'),
      ParameterName = Events.value('(Fields/Parameter[@Name="Name"]/@Value)[1]', 'varchar(20)'),
      ParameterDuration = Events.value('(Fields/Parameter[@Name="Duration"]/@Value)[1]', 'varchar(20)')
  FROM
      @XML.nodes('/EventSchedule/Event') AS XTbl(Events)
END
ELSE
BEGIN
  SELECT
      EventUID = Events.value('@Uid', 'int'),
      EventType = Events.value('@Type', 'varchar(20)'),
      EventKind = Events.value('(EventKind)[1]', 'varchar(20)'),
      ParameterType = Events.value('(Fields/Parameter[@Name="Type"]/@Value)[1]', 'varchar(20)'),
      ParameterName = Events.value('(Fields/Parameter[@Name="Name"]/@Value)[1]', 'varchar(20)'),
      ParameterDuration = Events.value('(Fields/Parameter[@Name="Duration"]/@Value)[1]', 'varchar(20)')
  FROM
      @XML.nodes('/EventSchedule/Event') AS XTbl(Events)
END