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I have a tabular representation of a relation called staff, I have been asked to complete a number of tasks like the degree and cardinality which is 5 and 3, but i have been asked why it is not meaningful to talk about the 2nd tuple in the relation and i have no idea why that would be the case.

*This is a practise exam, which came with no answers. Staff

Greg Hewgill
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user445714
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  • By looking at data I assume that the address length in 2nd tuple is more than the actual length defined. – Teja Mar 19 '12 at 20:08
  • Is the 2nd row specifically mentioned because the staffno 3124 is less than the other 2 row numbers, so on the outset it should have looked as though row 2 comes before row 1 and 3? – Mike Purcell Mar 19 '12 at 20:19

1 Answers1

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A tuple is to a relation as a row is to a table.

There is no notion of order in a relation (a relation is defined as an unordered set of tuples).

In a table (as you have displayed), order is an artifact of display - there is no concept of order in the relational model (although one could add the concept as an attribute of a tuple/row).

So there is no concept of the 1st, 2nd or 3rd tuple

Similarly, in a SQL RDBMS, order of returned rows is not guaranteed except where an ORDER BY is specified.

Cade Roux
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  • Thank you, i was just reading about the rule of insignificance of order but i couldnt relate to the tuple in that way. Thanks – user445714 Mar 19 '12 at 20:16