Multisets and aggregation Flashcards
1
Q
The multiplicity of an element describes its…
A
number of occurences
2
Q
______ on bags keeps duplicates
A
projection
3
Q
cartesian product on bags concatenates _______ as many times as they occur
A
tuples
4
Q
selection takes all occurences of tuples satisfying the _______
A
condition
5
Q
epsilon removes ______
A
duplicates
6
Q
____ adds multiplicities
A
union
7
Q
intersection takes the _______ multiplicity
A
minimum
8
Q
difference ______ multiplicities up to zero
A
subtracts
9
Q
SELECTα
A
πα(·)
10
Q
SELECT DISTINCT α
A
ε(πα(·))
11
Q
Q1 UNION ALL Q
A
Q1∪Q2
12
Q
Q1 UNION Q2
A
ε(Q1∪Q2)
13
Q
What are the 5 aggregate function in SQL?
A
COUNT, AVG, SUM, MIN, MAX
14
Q
What does GROUP BY do?
A
groups all common entries
15
Q
What is the order of evaluation in SQL (6 step)
A
FROM, WHERE, GROUP BY, AGGREGATES, HAVING, SELECT
