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As far as I understand NULLs were indeed a pragmatic choice, but the chief reason was the need to compute derived table values. E.g. in a join it is normal to g
by Mikhail_Edoshin 3y ago
As far as I understand NULLs were indeed a pragmatic choice, but the chief reason was the need to compute derived table values. E.g. in a join it is normal to get unknown values for a cell. This has to be expressed somehow. How? NULL seems to be a reasonably good generic solution to this. It may be possible to come up with a different generic solution, but such a solution would probably require something like conditional fields in a table and this is a whole new level of relational logic.
- cubefox 3y agoI wonder how Codd's original relational algebra handled this case, as he didn't have NULL cells.
- Mikhail_Edoshin 3y agoThis part I do not know, but NULLs are either Codd’s idea or the one he sided with. Another example when an invention goes against the established logic would be quaternions.
- at_compile_time 3y ago>Another example when an invention goes against the established logic would be quaternions. How so?
- bazoom42 3y agoI don’t think it had outer joins.