Question:
Consider a fact table in an OLAP application: Facts(D1, D2, val), where D1 and D2 are its dimension attributes and val is a dependent attribute. Suppose attribute D1 takes 3 values and D2 takes 2 values, and all combinations of these values are present in the table Facts. How many tuples are there in the result of the following query?
\[
\text{SELECT D1, D2, sum(val)}
\]
\[
\text{FROM Facts}
\]
\[
\text{GROUP BY CUBE (D1, D2);}
\]
Consider a fact table in an OLAP application: Facts(D1, D2, val), where D1 and D2 are its dimension attributes and val is a dependent attribute. Suppose attribute D1 takes 3 values and D2 takes 2 values, and all combinations of these values are present in the table Facts. How many tuples are there in the result of the following query?
\[
\text{SELECT D1, D2, sum(val)}
\]
\[
\text{FROM Facts}
\]
\[
\text{GROUP BY CUBE (D1, D2);}
\]
Show Hint
The CUBE operation in OLAP computes aggregates for all combinations of dimension values, including individual dimensions and the overall total.
Updated On: Apr 4, 2025
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The Correct Option is D
Solution and Explanation
The CUBE operation calculates the sum for all combinations of the values of \( D1 \) and \( D2 \), along with their respective totals:
For \( D1 \) with 3 values and \( D2 \) with 2 values, the total number of combinations is \( 3 \times 2 = 6 \).
In addition to these combinations, there are:
2 aggregates over \( D1 \),
3 aggregates over \( D2 \),
1 overall aggregate.
Thus, the total number of tuples is \( 6 + 2 + 3 + 1 = 12 \).
For \( D1 \) with 3 values and \( D2 \) with 2 values, the total number of combinations is \( 3 \times 2 = 6 \).
In addition to these combinations, there are:
2 aggregates over \( D1 \),
3 aggregates over \( D2 \),
1 overall aggregate.
Thus, the total number of tuples is \( 6 + 2 + 3 + 1 = 12 \).
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