如何获得总计数？

Question

我当前的查询按预期返回了每个种族的总人数，例如：

Name        |   Count
----------------------
White       |   22
Asian       |   15
Black       |   12

等等。但是我想添加一个第三列，它返回每个种族占总数的百分比，我该怎么做？

SELECT 
    eo.EthnicOriginName, 
    ISNULL(e.Number, '')
    --CAST(e.Number AS FLOAT) / CAST(COUNT(e.intEthnicOriginID) AS FLOAT)  * 100 

FROM 
    tblEthnicOrigin eo
    INNER JOIN tblPerson p ON p.intEthnicOriginID = eo.EthnicOriginID

    LEFT JOIN (SELECT intEthnicOriginID, COUNT(p.intPersonID) [Number]
            FROM tblPerson p
            INNER JOIN tblClient c on c.intPersonID = p.intPersonID
            GROUP BY intEthnicOriginID) e on e.intEthnicOriginID = eo.EthnicOriginID

GROUP BY
    eo.EthnicOriginName, e.Number

Answer 1

在大多数数据库中，您会使用 ANSI 标准的窗口函数：

SELECT eo.EthnicOriginName, COUNT(*) as num,
       COUNT(*) * 1.0 / SUM(COUNT(*)) OVER () as ratio
FROM tblEthnicOrigin eo INNER JOIN
     tblPerson p
     ON p.intEthnicOriginID = eo.EthnicOriginID
GROUP BY eo.EthnicOriginName;

* 1.0 只是因为有些数据库做整数除法，我们不希望整数除法。