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I'm looking at linked data in MS Access.
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)
I imagine there must be a good reason, and I would like to know it.
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In Access, a Yes/No field stores only two values: Yes or No. If you use a text box to display a Yes/No field, the value displays as -1 for Yes and 0 for No.
The Yes-No field is used to collect data with only a Yes or No answer. The field appears as a drop-down list on the canvas. The answer is stored in a database as a 1 or 0 where 1 = Yes and 0 = No. When writing Check Code, use (+) and (–) to indicate yes and no, respectively.
A value list is a hard-coded list of items that resides in the Row Source property of a list box or combo box control. In contrast, a lookup list takes its data from a lookup field (a field that uses a query to retrieve data from another table), and then loads that data into a combo box control.
A field's data type determines what kind of data it can store. MS Access supports different types of data, each with a specific purpose. The data type determines the kind of the values that users can store in any given field. Each field can store data consisting of only a single data type.
The binary representation of False is 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.
A bit of 1 at 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.
Let us change the sign of 1111111111111111. First invert; we get: 0000000000000000
Then add one: 0000000000000001, this is 1.
This is the proof that 1111111111111111 was the binary representation of -1.
UPDATE
Also, when comparing these values do not compare
x = -1 or
x = 1 instead, do compare
x <> 0 this always gives the correct result, independently of the convention used. Most implementations treat any value unequal zero as True.
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