Sql 如何在列中获取年数

我需要显示每个员工（ID，2011年、2012年、2013年、2014年）在各个年份的交易数量，我应该在年份编号下看到每年的交易数量，但现在我收到了以下表格：

我怎样才能改变它

我想我应该用WHERE，但我不知道怎么用

我目前的查询是：

SELECT oh.SalesPersonID AS perID, 
       YEAR(oh.OrderDate) AS [Year], COUNT(*)
FROM Sales.SalesOrderHeader oh 
JOIN Person.Person per ON oh.SalesPersonID = per.BusinessEntityID 
GROUP BY SalesPersonID, YEAR(OrderDate)
ORDER BY perID, [Year];

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只需使用条件聚合：

SELECT oh.SalesPersonID AS perID, 
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2011 THEN 1 ELSE 0 END) as cnt_2011,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2012 THEN 1 ELSE 0 END) as cnt_2012,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2013 THEN 1 ELSE 0 END) as cnt_2013,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2014 THEN 1 ELSE 0 END) as cnt_2014
FROM Sales.SalesOrderHeader oh JOIN
     Person.Person per
     ON oh.SalesPersonID = per.BusinessEntityID 
GROUP BY SalesPersonID
ORDER BY perID;

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只需使用条件聚合：

SELECT oh.SalesPersonID AS perID, 
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2011 THEN 1 ELSE 0 END) as cnt_2011,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2012 THEN 1 ELSE 0 END) as cnt_2012,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2013 THEN 1 ELSE 0 END) as cnt_2013,
       SUM(CASE WHEN YEAR(oh.OrderDate) = 2014 THEN 1 ELSE 0 END) as cnt_2014
FROM Sales.SalesOrderHeader oh JOIN
     Person.Person per
     ON oh.SalesPersonID = per.BusinessEntityID 
GROUP BY SalesPersonID
ORDER BY perID;

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回答得好。另一种可能是使用pivot查询，但我喜欢这个解决方案的简单性。回答不错。另一种方法可能是使用pivot查询，但我喜欢此解决方案的简单性。