访问“不正确"比较浮点数的操作.

本文介绍了访问“不正确"比较浮点数的操作.的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我正在Windows 7 64上使用MSAccess 2010.I am using MSAccess 2010 on Windows 7 64.我正在比较查询中的两个表.我要加入一个复合PK并选择其中表A列A<>表B列A所在的行，其中两个表的A列都为double.I am comparing two tables in a query. I am joining on a composite PK and selecting rows where table A column A <> table B column A where column A for both tables is a double.它可以工作120行.对于28行，表A列A的值为0.088 表B列A的0.088.For 120 rows it works. For 28 rows a value of 0.088 in table A column A <> 0.088 in table B column A.在任何地方都没有使用文本函数.There are no text functions used ANYWHERE.当我向查询中添加列时:[TableA]！[ColumnA]-[TableB]！[ColumnA]我返回的值类似于-1.38777878078145E-17.When I add a column to the query a:[TableA]![ColumnA] - [TableB]![ColumnA] I return values like -1.38777878078145E-17.当我将查询导出到Excel并进行数学运算时，结果= 0.When I export the query to Excel and do the math the result = 0. 0.088-0.088<> 0怎么可能?0.088 double<> 0.088 double是怎么可能的?How is it possible that 0.088 - 0.088 <> 0?How is it possible that 0.088 double <> 0.088 double?推荐答案这是一个非常普遍的问题，与任何计算上下文(不仅仅是Access)中的浮点数的性质有关.看起来像是一个悖论，但事实是Double值可以近似表示非常广泛的数字范围(最多15个有效数字，参考:此处)，但是表示几乎从来都不是精确.这就是为什么:This is a very common problem related to the nature of floating-point numbers in any computing context (not just Access). It seems like a paradox, but the fact is that a Double value can approximately represent a huge range of numbers very precisely (up to 15 significant digits, ref: here), but that representation is almost never exact. That's why: 精确比较浮点数(例如x=y)有时可能会失败，因此exact comparisons of floating numbers (e.g. x=y) can sometimes fail, and therefore您永远不应依赖两个Double字段之间的JOIN.you should never rely on a JOIN between two Double fields.有关浮点数的更多信息，请此处. Wikipedia还可以在此处解决该问题.More information on floating-point numbers is available here. Wikipedia also addresses the issue here.如果您的字段的小数位数需要精确比较，那么您可能需要考虑将其更改为Currency或Decimal.If you have fields with decimal places that require exact comparisons then you may want to consider changing them to Currency or Decimal. 这篇关于访问“不正确"比较浮点数的操作.的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！