如何获取列中的年份数字

Question

我需要显示单个员工在各个年份的交易次数（ID，2011、2012、2013、2014），并且应该在年份编号下查看每年的交易次数，但是现在我收到此表格：

如何更改它？

我认为我应该使用WHERE，但我不知道该怎么做

我当前的查询是：

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];

Answer 1

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;