Geek Answers Handbook

Attributes without Attributes

Aheo asks if there is ok for a single column table . How about one without columns, or given that it seems difficult for most modern "relational" DBMSs, a relationship without attributes?

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DEE and the Cartesian product form a monoid. In practice, if you have a relational date representation operator, you should use DEE as a grouping relation to get totals. There are many other examples where DEE is practically useful, for example. in a functional setting with a binary join operator you get n-ary join = foldr join dee

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" : . " "Date Darwen () TABLE_DEE TABLE_DUM ().

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cjs=> CREATE TABLE D ();
CREATE TABLE
cjs=> SELECT COUNT (*) FROM D;
 count 
-------
     0
(1 row)

cjs=> INSERT INTO D () VALUES ();
ERROR:  syntax error at or near ")"
LINE 1: INSERT INTO D () VALUES ();
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TABLE_DEE TABLE_DUM SQL. , , db .

It is also difficult to see the usefulness of TABLE_DEE and TABLE_DUM in relational algebra. Need to look beyond that. To get an idea of ​​how these constants can come to life, consider a relational algebra placed in the proper mathematical form, which is as close as possible for Boolean algebra. D & D Algebra A is a step in that direction. Then we can express the classical operations of relational algebra in terms of more fundamental ones, and these two constants will become really convenient.

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