查询空字段 [英] Query for empty fields
问题描述
您好，
我必须在Access查询中获取一个值，该值取决于我是否有一个空字段，而我无法获得解决方案以便正确决定IF条款
当前不起作用的查询如下：
Hello,
I have to get a value in an Access query that depends on if I have one empty field, and I cannot get the solution in order to decide the "IF" clause correctly
The current query that does not work is as follows:
DelayDays: (if([RealDate]=0;[PlannedDate];[RealDate])-[CommitedDate])
日期是日期格式，减法有效好吧，但在某些情况下，我在数据库中将[RealDate]字段清空，然后我得到DelayDays为空字段的结果。
然后，我的问题是if子句总是执行为false。因此，当字段[RealDate]为空时，它无法进行计算并返回空字段（不是错误）。
我也尝试过其他选项Access接受if语句中的有效比较，例如
The dates are in date format, and the substraction works well, but in some cases I have the [RealDate] field empty in the database, and then I get as result for "DelayDays" an empty field.
Then, my problem is that the "if" clause is always executed as "false". Thus when the field[RealDate] is empty, it can not make the calculation and returns an empty field (not an error).
I have also tried with other options that the Access accept as valid comparisons within the "if" statement, like
[RealDate]<1
isempty([RealDate])等，但我没有办法检测该字段是空的还是没有价值。
任何帮助都将受到高度赞赏。
提前谢谢，
David
etc, but I do not get a way of detecting when the field is empty or has no value.
Any help will be highly appreciated.
Thank you in advance,
David
推荐答案
假设空表示空，请查看 IsNull [< a href =http://www.techonthenet.com/access/functions/advanced/isnull.phptarget =_ blanktitle =新窗口> ^ ]功能：用它来替换值合理的默认值。
http://office.microsoft.com/en-gb/access-help/examples-of-expressions-that-check-for-null-values- HP001099035.aspx [ ^ ]
Assuming by "empty" you mean "null", look at the IsNull[^] function: use it to replace the values with "sensible" defaults.
http://office.microsoft.com/en-gb/access-help/examples-of-expressions-that-check-for-null-values-HP001099035.aspx[^]
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