Boolean Logic 101 - Feel free to skip if this is not your thread!
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In addition to other replies - Boolean logic is interesting in that it has no real arithmetic value and can have only true or false
as a value. It doesn't fit too well as a high-level storage value of a system even though it permeates low-level storage in every
way - it can't be null for instance, but in an RDBMS it _can_ be Null and it _can_ be arithmetic by taking on the values 0 and 1
for false and true respectively. This has the added advantage that it can be used in arithmetic statements which is what Igor used
to save considerable amounts of typing in your query.
Whether or not it is faster in execution than a case statement is probably up to some testing, but I am willing to bet it is
somewhat faster considering the relative complexity of a CASE statement.
Any statement containing a comparison operator ends up being a Boolean statement because it can be found to either be so, or not be
so. Month is not Boolean, but (Month = January) is definitely Boolean, because the comparison is either true or false depending on
the value of "Month".
Similarly any attribute can be Boolean if it is found to be an attribute of an object. Giuseppe is not Boolean, but he is human and
likely male, so that:
(Giuseppe = Human) is true or 1, and
(Giuseppe = Female) is false or 0.
For RDBMS and indeed most programming languages, any Boolean evaluated result can directly be inferred as the arithmetic values 0
and 1 so that I could make some programmatic assumptive statements based on it, such as:
HumanX's fertility period recurs every (28 * (HumanX = Female)) days. This will be 0 days for men (28 * false) = (28 * 0) = 0, and
28 for ladies as (28 * true) = (28 * 1) = 28 in the same logic.
Similarly your odds of balding is roughly 0.04 + (35/Age)*((HumanX = Male) * 10) since men have a roughly 40% chance of balding by
age 35 which is about 10 times more likely than women and the odds increase with age[1].
Hope this makes clear how Booleans are used mathematically in high-level code.
Have a great day!
Ryan
[1] - http://www.statisticbrain.com/hair-loss-statistics/
On 2013/12/21 22:24, Giuseppe Costanzi wrote:
...but stats.which_month is not a boolean, it represent a month...
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