DATA 520 Databases Class Notes (Fall 2024)
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Thursday, November 21, 2024
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Week 12
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select cname as cn from customer ;

select * from customer where city='Kyoto';

select * from product
  where city='Dallas' and price>0.50;

select aid from agent where percent >= 6;

T1 := (R∪S)
T2 := (R∩S)
T  := T1–T2

T  =
a2 	b1 	c2
a1 	b1 	c2
a3 	b2 	c3


Thursday, November 14, 2024
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Week 12
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Table = Set

superset
subset

key = sid

superkey = {sid, lname}

|Domain(City)|: 1000

Duluth
GF
Fargo
Paris
London
...

|Domain(CID)|: 100

  Domain(City) x Domain(CID) : Cartesian Product 
= 10 x 1000 = 10**4

  Domain(US City) x Domain(CID)
= 500 x 100 = 5 x 10**4

  select cid, title from buy y, book b
    where y.cid = 10 and y.ISBN = b.ISBN;

  |domain(buy)|  = 1000
  |domain(book)| = 10000

  |domain(buy) x domain(book)|
= 1000 x 10000
= 10**7

  for ( i = 1; i < |domain(buy)|; i++)
    for ( j = 1; j < |domain(book)|; j++ )
      if (y.cid = 10 and y.ISBN = b.ISBN)
        then print cid, title

 select KEY from dependent;