如何使用 PIVOT 在 SQL 中动态生成和填充带有计数值的列？

SQL动态列生成与计数填充

在SQL中动态创建列并用计数值填充它们，通常使用PIVOT函数。

静态列生成:

如果列数已知，可以在PIVOT语句中使用硬编码值：

<code class="language-sql">SELECT name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
FROM
(
  SELECT c.name, cr.description, r.typeid
  FROM customers c
  LEFT JOIN rewards r ON c.id = r.customerid
  LEFT JOIN customerrewards cr ON r.typeid = cr.typeid
) x
PIVOT
(
  COUNT(typeid) FOR description IN ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
) p;</code>

动态列生成:

对于未知数量的列，可以使用动态SQL：

<code class="language-sql">DECLARE @cols AS NVARCHAR(MAX),
    @query AS NVARCHAR(MAX)

SELECT @cols = STUFF((SELECT ',' + QUOTENAME(description)
                    FROM customerrewards
                    GROUP BY description, typeid
                    ORDER BY typeid
            FOR XML PATH(''), TYPE
            ).VALUE('.', 'NVARCHAR(MAX)')
        ,1,1,'')

SET @query = 'SELECT name,' + @cols + ' FROM
             (
                SELECT c.name, cr.description, r.typeid
                FROM customers c
                LEFT JOIN rewards r ON c.id = r.customerid
                LEFT JOIN customerrewards cr ON r.typeid = cr.typeid
            ) x
            PIVOT
            (
                COUNT(typeid) FOR description IN (' + @cols + ')
            ) p '

EXECUTE(@query)</code>

包含总计列:

要添加总计列，可以使用ROLLUP函数：

静态版本:

<code class="language-sql">SELECT name, SUM([Bronze]) Bronze, SUM([Silver]) Silver, 
  SUM([Gold]) Gold, SUM([Platinum]) Platinum, SUM([AnotherOne]) AnotherOne
FROM 
(
  SELECT name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
  FROM
  (
    SELECT c.name, cr.description, r.typeid
    FROM customers c
    LEFT JOIN rewards r ON c.id = r.customerid
    LEFT JOIN customerrewards cr ON r.typeid = cr.typeid
  ) x
  PIVOT
  (
    COUNT(typeid) FOR description IN ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
  ) p
) x
GROUP BY name WITH ROLLUP</code>

动态版本:

<code class="language-sql">DECLARE @cols AS NVARCHAR(MAX),
    @colsRollup AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

SELECT @cols = STUFF((SELECT ',' + QUOTENAME(description) 
                    FROM customerrewards
                    GROUP BY description, typeid
                    ORDER BY typeid
            FOR XML PATH(''), TYPE
            ).VALUE('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

SELECT @colsRollup 
      = STUFF((SELECT ', SUM(' + QUOTENAME(description) + ') AS '+ QUOTENAME(description)
                    FROM customerrewards
                    GROUP BY description, typeid
                    ORDER BY typeid
            FOR XML PATH(''), TYPE
            ).VALUE('.', 'NVARCHAR(MAX)') 
        ,1,1,'')


SET @query 
          = 'SELECT name, '+ @colsRollup + '
             FROM
             (
                SELECT name,' + @cols + ' FROM 
                 (
                    SELECT c.name, cr.description, r.typeid
                    FROM customers c
                    LEFT JOIN rewards r ON c.id = r.customerid
                    LEFT JOIN customerrewards cr ON r.typeid = cr.typeid
                ) x
                PIVOT 
                (
                    COUNT(typeid) FOR description IN (' + @cols + ')
                ) p 
              ) x1
              GROUP BY name WITH ROLLUP'

EXECUTE(@query)</code>

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