SQL 为什么 MS Access 数据库中“是”的值为 -1？
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Why is "Yes" a value of -1 in MS Access database?
提问by supermitch
I'm looking at linked data in MS Access.
我正在查看 MS Access 中的链接数据。
The "Yes/No" fields contain the value -1 for YES and 0 for NO. Can someone explain why such a counter-intuitive value is used for "Yes"? (Obviously, it should be 1 and 0)
“是/否”字段包含值 -1 表示 YES 和 0 表示否。有人可以解释为什么这样一个违反直觉的值用于“是”？（显然，它应该是 1 和 0）
I imagine there must be a good reason, and I would like to know it.
我想一定有一个很好的理由，我很想知道。
回答by Olivier Jacot-Descombes
The binary representation of Falseis 0000000000000000(how many bits are used depends on the implementation). If you perform a binary NOT operation on it, it will be changed to 1111111111111111, i.e. True, but this is the binary representation of the signed integer -1.
的二进制表示False是0000000000000000（使用多少位取决于实现）。如果对其执行二进制 NOT 运算，它将更改为1111111111111111，即True，但这是有符号整数的二进制表示-1。
A bit of 1at the most significant position signals a negative number for signed numbers. Changing the sign of a number happens by inverting all the bits and adding 1. This is called the Two's complement.
的位1在最显著位置信号的符号数为负数。通过反转所有位并加 1 来更改数字的符号。这称为二进制补码。
Let us change the sign of 1111111111111111. First invert; we get:
0000000000000000
让我们改变 的符号1111111111111111。第一次反转；我们得到：
0000000000000000
Then add one:
0000000000000001, this is 1.
然后加一个：
0000000000000001，这是1。
This is the proof that 1111111111111111was the binary representation of -1.
这是 的1111111111111111二进制表示的证明-1。
UPDATE
更新
Also, when comparing these values do not compare
此外，在比较这些值时，不要比较
x = -1
or
或者
x = 1
instead, do compare
相反，做比较
x <> 0
this always gives the correct result, independently of the convention used. Most implementations treat any value unequal zero as True.
这总是给出正确的结果，与使用的约定无关。大多数实现将任何不等于零的值视为True。
回答by cdeszaq
"Yes" is -1 because it isn't anything else.
“是”是 -1，因为它不是其他任何东西。
When dealing with Microsoft products, especially one as old as Access, don't assume that there is a good reason for anydesign choice.
在处理 Microsoft 产品时，尤其是像 Access 一样古老的产品时，不要假设任何设计选择都有充分的理由。
