执行下面两个操作：
1、
SELECT DISTINCT soh .CustomerID ,MIN(soh .OrderDate)
FROM Sales .SalesOrderHeader soh
GROUP BY CustomerID
ORDER BY CustomerID
2、
SELECT soh .CustomerID ,soh .SalesOrderID ,soh .OrderDate我想问一下，为什么两种处理结果的显示数目会不一样，我感觉应该一样都对！！！！
FROM Sales .SalesOrderHeader soh
WHERE soh .OrderDate = (SELECT MIN(soh2.OrderDate) FROM Sales .SalesOrderHeader soh2
WHERE soh2.CustomerID =soh .CustomerID
)
ORDER BY CustomerID
------解决思路----------------------
必须不一样，MIN(soh2.OrderDate)，如果有两条，第一个语句只会出现一条，而第二个语句会有两条