Suppose ORACLE relation 𝑅(𝐴,𝐵) currently has tuples {(1,2),(1,3),(3,4)} and…
2015
Suppose ORACLE relation 𝑅(𝐴,𝐵) currently has tuples {(1,2),(1,3),(3,4)} and relation 𝑆(𝐵,𝐶) currently has {(2,5),(4,6),(7,8)}.Consider the following two SQL queries SQ1 and SQ2:
SQ1: Select *
From R Full Join S
On R.B=S.B;
SQ2: Select *
From R Inner Join S
On R.B=S.B;
The numbers of tuples in the result of the SQL query SQ1 and the SQL query SQ2 are given by:
- A.
2 and 6 respectively
- B.
6 and 2 respectively
- C.
2 and 4 respectively
- D.
4 and 2 respectively
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Correct answer: D
Given: R has tuples (1,2), (1,3), (3,4).
S has tuples (2,5), (4,6), (7,8).
Matches on column B:
B = 2 gives the joined row (1,2,5).
B = 4 gives the joined row (3,4,6).
Unmatched rows that appear only in one relation:
From R: (1,3) has no matching B in S, so it appears as (1,3,NULL) in the full join.
From S: (7,8) has no matching B in R, so it appears as (NULL,7,8) in the full join.
Counts:
Full join result has 4 tuples (2 matched + 1 unmatched from R + 1 unmatched from S).
Inner join result has 2 tuples (the two matched rows).
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