1. Registered User
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## Relational Algebra

I am trying to learn relational algebra. Take the following equation;

σ F ( r ) = { t ∣ t ∈ r ∧ F ( t ) } σ

What does "∣" represent in this equation?
What does "∧" represent?
What do the braces { } represent?
What do the brackets ( ) represent?
What would be your "plain english" interpretation of this equation?
Here is the Web page that is the source of this equation.
Thanks.

2. Registered User
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∧ means "AND".
t means "tuple t"
Brackets and braces are just parentheses.
In English "For all tuples t where t is a member of r AND F(t) is TRUE". This is a definition of restiction (σ) which they call "select".

You should find a textbook with clearer explanations. "The Alice Book" is a classic (http://www.amazon.com/Foundations-Da...dp/0201537710/) but it is VERY heavy on the maths. A more accessible book is Chris Date's "Introduction to Database Systems".

3. SQL Consultant
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Originally Posted by dportas
A more accessible book is Chris Date's "Introduction to Database Systems".
i guess you didn't see enuenu's other thread, then

4. Registered User
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Seen it now, thanks.

5. Registered User
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Thanks all. I will check the text out. My baptism of fire is cooling a little now. It has been a while since I did any real maths.

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