TSQL的连乘

某个需求需要对某一列的值做乘法，网上搜了把确实还真没有直接的聚合函数用于将某一列的值乘起来。

找到了替代的算法：

http://jerryyang-wxy.blogspot.com/2012/04/transact-sql.html

http://blog.csdn.net/walkbob/article/details/45508501

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新问题出现了：如果要做连乘的那一列出现了0的值或者是小于0的值，做LOG运算时会出现

An invalid floating point operation occurred.的错误

下面这个例子用于解决某列的值有小于等于零的值而又要做连乘的TSQL：

--生成测试表
DROP TABLE #T
SELECT 1 AS A INTO #T
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 0
UNION ALL SELECT -1
UNION ALL SELECT -2
UNION ALL SELECT -3
UNION ALL SELECT -4
UNION ALL SELECT -5
--定义三个参数，用于分别计算大于0的值，等于0的值，小于0的值的连乘结果
declare @oZero as decimal(12,0)
declare @eZero as decimal(12,0)
declare @lZero as decimal(12,0)
--大于0的值
select @oZero = ISNULL(POWER(10.0,SUM(LOG(A))),1)
FROM #T
WHERE A > 0
--等于0的值（相加即可）
select @eZero = isnull(sum(A),1)
FROM #T
WHERE A = 0
--小于0的值
select @lZero = ISNULL(POWER(10.0,SUM(LOG10(A*-1))),1)*power(-1,(count(1)))
FROM #T
WHERE A < 0
--三个结果相乘
select @oZero * @eZero * @lZero as result