从 XML 消息和数据库表中连接数据

可以使用与消息数据和数据库都进行交互的 SELECT 语句。 还可以嵌套 SELECT 语句,该语句与另一个 SELECT 语句中的一种数据类型进行交互,而该另一个 SELECT 语句又与其他类型的数据进行交互。

请参阅下列包含两个客户发票信息的输入消息:

<Data>
  <Invoice>
    <CustomerNumber>1234</CustomerNumber>
    <Item>
      <PartNumber>1</PartNumber>
      <Quantity>9876</Quantity>
    </Item>
    <Item>
      <PartNumber>2</PartNumber>
      <Quantity>8765</Quantity>
    </Item>
</Invoice>
  <Invoice>
    <CustomerNumber>2345</CustomerNumber>
    <Item>
      <PartNumber>2</PartNumber>
      <Quantity>7654</Quantity>
    </Item>
    <Item>
      <PartNumber>1</PartNumber>
    <Quantity>6543</Quantity>
    </Item>
</Invoice>
</Data>

请参阅下列数据库表 Prices 和 Addresses 以及它们的内容:

PARTNO      PRICE                   
----------- ------------------------
                    1            +2.50000E+001
                    2            +6.50000E+00



PARTNO      STREET                CITY             COUNTRY  
------      -------------------   --------------   ------- 
1234        22 Railway Cuttings   East Cheam       England
2345        The Warren            Watership Down   England

如果您对下列 ESQL 转换进行编码:

-- Create a valid output message
SET OutputRoot.MQMD = InputRoot.MQMD;

-- Select suitable invoices
SET OutputRoot.XML.Data.Statement[] =
      (SELECT I.CustomerNumber                         AS Customer.Number,
                      A.Street                                 AS Customer.Street,
                      A.City                                   AS Customer.Town,
                      A.Country                                AS Customer.Country,

                -- Select suitable items
                    (SELECT II.PartNumber AS PartNumber,
                              II.Quantity   AS Quantity,
                                    PI.Price      AS Price
                      FROM Database.db2admin.Prices AS PI,
                              I.Item[]                 AS II
                      WHERE II.PartNumber = PI.PartNo     )    AS Purchases.Item[]
      
        FROM Database.db2admin.Addresses  AS A,
                  InputRoot.XML.Data.Invoice[] AS I
           
        WHERE I.CustomerNumber = A.PartNo
    );

生成下列输出消息:输入消息已增加了从数据库表中获取的价格和地址信息:

<Data>
  <Statement>
    <Customer>
      <Number>1234</Number>
      <Street>22 Railway Cuttings</Street>
      <Town>East Cheam</Town>
      <Country>England</Country>
    </Customer>
    <Purchases>
      <Item>
        <PartNumber>1</PartNumber>
        <Quantity>9876</Quantity>
        <Price>2.5E+1</Price>
      </Item>
      <Item>
        <PartNumber>2</PartNumber>
        <Quantity>8765</Quantity>
        <Price>6.5E+1</Price>
      </Item>
    </Purchases>
  </Statement>
  <Statement>
    <Customer>
      <Number>2345</Number>
      <Street>The Warren</Street>
      <Town>Watership Down</Town>
      <Country>England</Country>
    </Customer>
    <Purchases>
      <Item>
        <PartNumber>1</PartNumber>
        <Quantity>6543</Quantity>
        <Price>2.5E+1</Price></Item>
      <Item>
        <PartNumber>2</PartNumber>
        <Quantity>7654</Quantity>
        <Price>6.5E+1</Price>
      </Item>
    </Purchases>
  </Statement>
</Data>

可以在消息 SELECT 语句中嵌套数据库 SELECT。在多少情况下,这不然前一个示例有效,但是您可能发现如果消息小而数据库表大,这个比较好。

-- Create a valid output message
SET OutputRoot.MQMD = InputRoot.MQMD;

-- Select suitable invoices
SET OutputRoot.XML.Data.Statement[] =
       (SELECT I.CustomerNumber                         AS Customer.Number,

                -- Look up the address
                THE ( SELECT 
                                    A.Street,
                                    A.City    AS Town,
                                    A.Country
                                FROM Database.db2admin.Addresses AS A
                                WHERE A.PartNo = I.CustomerNumber
                        )                             AS Customer,

                -- Select suitable items
               (SELECT
                        II.PartNumber AS PartNumber,
                        II.Quantity   AS Quantity,

                        -- Look up the price
                        THE (SELECT ITEM P.Price
                            FROM Database.db2admin.Prices AS P
                            WHERE P.PartNo = II.PartNumber
                        )             AS Price               

                    FROM I.Item[] AS II           ) AS Purchases.Item[]
      
         FROM InputRoot.XML.Data.Invoice[] AS I
    );
相关概念
消息流概述
ESQL 概述
消息建模
相关任务
设计消息流
定义消息流内容
管理 ESQL 文件
相关参考
Compute 节点
Database 节点
Filter 节点
ESQL 引用
SELECT 函数
SET 语句
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