使用SQL根据硬编码数字对XML输出进行分组

如何解决使用SQL根据硬编码数字对XML输出进行分组

我正在查询一个以XML格式提供输出的查询。

DECLARE @XMLDATA1 XML 
SET @XMLDATA1 = (


SELECT StudentId AS 'StudentID',StudentName AS 'StudentName',StudentAge AS 'Age',StudentYear 'Year'

FROM Student 
ORDER BY StudentId
FOR XML PATH('StudentLine')
)

SELECT ( CAST(@XMLDATA1 AS XML ))
FOR XML PATH ('StudentRecords'),Root('Student')

示例输出如下。

<StudentRecords>
    <Student>
        <StudentLine>
            <StudentID>12</StudentID>
            <StudentName>Kevin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
        <StudentLine>
            <StudentID>13</StudentID>
            <StudentName>Peter</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
        <StudentLine>
            <StudentID>14</StudentID>
            <StudentName>Martin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
        <StudentLine>
            <StudentID>15</StudentID>
            <StudentName>Justin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
    </Student>
</StudentRecords>

我想基于sql查询中的硬编码数字从<StudentRecords>标记中拆分这些记录。作为示例，如果我想拆分为3条记录，那么xml将如下所示。

<StudentRecords>
    <Student>
        <StudentLine>
            <StudentID>12</StudentID>
            <StudentName>Kevin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
        <StudentLine>
            <StudentID>13</StudentID>
            <StudentName>Peter</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
        <StudentLine>
            <StudentID>14</StudentID>
            <StudentName>Martin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
    </Student>
</StudentRecords>
<StudentRecords>
    <Student>
        <StudentLine>
            <StudentID>15</StudentID>
            <StudentName>Justin</StudentName>
            <Age>10</Age>
            <Year>5</Year>
        </StudentLine>
    </Student>
</StudentRecords>

在某些情况下，例如带有100000 <StudentLine>标签的记录，而硬编码的数量可以是2000。 有人可以帮助我实现这一目标。 谢谢。

解决方法

这是如何通过XQuery和FLWOR表达式实现它。

• 组中的行数将作为输入参数。
• 我们将使用NTILE()函数根据数字创建组 组中的行数。
• FLWOR表达式有两个循环：（1）遍历组，（2）遍历给定组中的<StudentLine>元素。

SQL

-- DDL and sample data population,start
DECLARE @tbl TABLE (StudentID INT PRIMARY KEY,StudentName VARCHAR(30),Age INT);
INSERT INTO @tbl (StudentID,StudentName,Age) VALUES
(1,'Martha',10),(2,'Boris',12),(3,'Judy',15),(12,'Kevin',19),(13,'Peter',(14,'Martin',18),(15,'Justin',25);
-- DDL and sample data population,end

-- denominator specifies # of rows in a group
DECLARE @NumOfGroups DECIMAL(10,1) = (SELECT COUNT(*) FROM @tbl) / 3.0;
SET @NumOfGroups = CEILING(@NumOfGroups);

-- just to see
SELECT groupId = NTILE(CAST(@NumOfGroups AS INT)) OVER (ORDER BY StudentID),*
FROM @tbl;

SELECT (
    SELECT groupID = NTILE (CAST(@NumOfGroups AS INT)) OVER (ORDER BY StudentID),*
    FROM @tbl
    FOR XML PATH('StudentLine'),TYPE,ROOT('root')
).query('

    for $gr in distinct-values(/root/StudentLine/groupID/text())
    return <StudentRecords>
                <Student>
            {
                for $x in /root/StudentLine[(groupID/text())[1] eq $gr]
                return $x
            }
        </Student>
    </StudentRecords>

');

输出

  <StudentRecords>
    <Student>
      <StudentLine>
        <groupID>1</groupID>
        <StudentID>1</StudentID>
        <StudentName>Martha</StudentName>
        <Age>10</Age>
      </StudentLine>
      <StudentLine>
        <groupID>1</groupID>
        <StudentID>2</StudentID>
        <StudentName>Boris</StudentName>
        <Age>12</Age>
      </StudentLine>
      <StudentLine>
        <groupID>1</groupID>
        <StudentID>3</StudentID>
        <StudentName>Judy</StudentName>
        <Age>15</Age>
      </StudentLine>
    </Student>
  </StudentRecords>
  <StudentRecords>
    <Student>
      <StudentLine>
        <groupID>2</groupID>
        <StudentID>12</StudentID>
        <StudentName>Kevin</StudentName>
        <Age>19</Age>
      </StudentLine>
      <StudentLine>
        <groupID>2</groupID>
        <StudentID>13</StudentID>
        <StudentName>Peter</StudentName>
        <Age>10</Age>
      </StudentLine>
    </Student>
  </StudentRecords>
  <StudentRecords>
    <Student>
      <StudentLine>
        <groupID>3</groupID>
        <StudentID>14</StudentID>
        <StudentName>Martin</StudentName>
        <Age>18</Age>
      </StudentLine>
      <StudentLine>
        <groupID>3</groupID>
        <StudentID>15</StudentID>
        <StudentName>Justin</StudentName>
        <Age>25</Age>
      </StudentLine>
    </Student>
  </StudentRecords>

,

这对我有用，而无需FLWOR

-- DDL and sample data population,1) = (SELECT COUNT(*) FROM @tbl) / 3.0;
SET @NumOfGroups = CEILING(@NumOfGroups);

-- no FLWOR used
WITH c AS   (
            SELECT groupID = NTILE (CAST(@NumOfGroups AS INT)) OVER (ORDER BY StudentID),*
            FROM @tbl
            )
SELECT      (   SELECT      StudentID,Age
                FROM        c
                WHERE       c.groupID = g.groupID
                FOR XML     PATH('StudentLine'),TYPE   ) AS Student
FROM        (
            SELECT DISTINCT groupID FROM c
            ) g
FOR XML     PATH('')