尝试循环通过 XML 提取 PLSQL 中的值

Question

我正在尝试遍历 XML 并提取 UUID。我有以下内容，它循环正确的次数并每次打印一个空白行。为什么不提取 UUID 节点的文本值？

   DECLARE
       X XMLTYPE := XMLTYPE('<?xml version="1.0" ?> 
         <StatusUp>
           <G_UUIDs>
               <UUID>1 test 1</UUID>
               <UUID>2 test 2</UUID>
               <UUID>3 test 3 </UUID>
               <UUID>4 test 4 </UUID>
           </G_UUIDs>
        </StatusUp>');
    BEGIN
       FOR r IN (SELECT EXTRACTVALUE(VALUE(p), 'StatusUp/G_UUIDs/UUID/text()') AS uuid

                   FROM TABLE(XMLSEQUENCE(EXTRACT(X, '//StatusUp/G_UUIDs/UUID'))) p)
       LOOP
          DBMS_OUTPUT.PUT_LINE('UUID' || r.uuid);
       END LOOP;
    END;

Answer 1

您已经在 FROM 语句中从 XML 中提取了 UUID，而在 select 中，形象地说，您现在只有四行

<UUID> n test n </UUID>

所以提取数据的正确方法是：

DECLARE
  X XMLTYPE := XMLTYPE(
    '<?xml version="1.0" ?> 
    <StatusUp>
      <G_UUIDs>
        <UUID>1 test 1</UUID>
        <UUID>2 test 2</UUID>
        <UUID>3 test 3 </UUID>
        <UUID>4 test 4 </UUID>
      </G_UUIDs>
    </StatusUp>');
BEGIN
  FOR r IN (SELECT
              EXTRACTVALUE(
                VALUE(p),
                --'StatusUp/G_UUIDs/UUID/text()') AS uuid
                '/UUID/text()') AS uuid
            FROM
              TABLE(
                XMLSEQUENCE(
                  EXTRACT(
                    X,
                    '//StatusUp/G_UUIDs/UUID')
                )
              ) p
           )
  LOOP
    DBMS_OUTPUT.PUT_LINE(r.uuid);
  END LOOP;
END;

Answer 2

如果您要将其转换为 sql 语句并运行它，如下所示：

WITH sample_data AS (SELECT XMLTYPE('<?xml version="1.0" ?> 
         <StatusUp>
           <G_UUIDs>
               <UUID>1 test 1</UUID>
               <UUID>2 test 2</UUID>
               <UUID>3 test 3 </UUID>
               <UUID>4 test 4 </UUID>
           </G_UUIDs>
        </StatusUp>') x FROM dual)
SELECT p.*,
       EXTRACTVALUE(VALUE(p), 'StatusUp/G_UUIDs/UUID/text()') AS uuid
FROM   sample_data sd,
       TABLE(XMLSEQUENCE(EXTRACT(sd.x, '//StatusUp/G_UUIDs/UUID'))) p;

很容易发现问题：

COLUMN_VALUE             UUID
------------------------ ----------
<UUID>1 test 1</UUID>
<UUID>2 test 2</UUID>
<UUID>3 test 3 </UUID> 
<UUID>4 test 4 </UUID>

即您正在尝试从仅包含节点 UUID 的 xml 中提取节点 StatusUp/G_UUIDs/UUID。相反，如果您更正要查询的节点，您会得到正确的结果：

DECLARE
   X XMLTYPE := XMLTYPE('<?xml version="1.0" ?> 
     <StatusUp>
       <G_UUIDs>
           <UUID>1 test 1</UUID>
           <UUID>2 test 2</UUID>
           <UUID>3 test 3 </UUID>
           <UUID>4 test 4 </UUID>
       </G_UUIDs>
    </StatusUp>');
BEGIN
   FOR r IN (SELECT EXTRACTVALUE(VALUE(p), 'UUID/text()') AS uuid
               FROM TABLE(XMLSEQUENCE(EXTRACT(X, '//StatusUp/G_UUIDs/UUID'))) p)
   LOOP
      DBMS_OUTPUT.PUT_LINE('UUID' || r.uuid);
   END LOOP;
END;
/

UUID1 test 1
UUID2 test 2
UUID3 test 3 
UUID4 test 4 

但是，不推荐使用 EXTRACT 和 EXTRACTVALUE - 您应该改用 XMLTABLE：

DECLARE
   X XMLTYPE := XMLTYPE('<?xml version="1.0" ?> 
     <StatusUp>
       <G_UUIDs>
           <UUID>1 test 1</UUID>
           <UUID>2 test 2</UUID>
           <UUID>3 test 3 </UUID>
           <UUID>4 test 4 </UUID>
       </G_UUIDs>
    </StatusUp>');
BEGIN
   FOR r IN (SELECT *
             FROM   XMLTABLE('//StatusUp/G_UUIDs/UUID'
                             PASSING x
                             COLUMNS uuid varchar2(10) PATH '.'))
   LOOP
      DBMS_OUTPUT.PUT_LINE('UUID' || r.uuid);
   END LOOP;
END;
/

UUID1 test 1
UUID2 test 2
UUID3 test 3 
UUID4 test 4 

---

您应该尝试运行的等效查询：

WITH sample_data AS (SELECT XMLTYPE('<?xml version="1.0" ?> 
         <StatusUp>
           <G_UUIDs>
               <UUID>1 test 1</UUID>
               <UUID>2 test 2</UUID>
               <UUID>3 test 3 </UUID>
               <UUID>4 test 4 </UUID>
           </G_UUIDs>
        </StatusUp>') x FROM dual)
SELECT *
FROM   sample_data sd,
       XMLTABLE('//StatusUp/G_UUIDs/UUID'
                PASSING sd.x
                COLUMNS uuid varchar2(10) PATH '.');