Podcast
Questions and Answers
What does the function COUNT(DISTINCT x) do?
What does the function COUNT(DISTINCT x) do?
- Counts all tuples regardless of duplicates.
- Calculates the average of attribute x.
- Sums the values of attribute x only.
- Counts the total number of distinct tuples for the attribute x. (correct)
Which of the following aggregation functions cannot be used in the WHERE clause?
Which of the following aggregation functions cannot be used in the WHERE clause?
- `SUM(x)`
- `AVG(x)`
- `MAX(x)`
- All of the above (correct)
If you want to find the minimum value of an attribute x, which function should you use?
If you want to find the minimum value of an attribute x, which function should you use?
- `MIN(x)` (correct)
- `AVERAGE(x)`
- `SUM(x)`
- `COUNT(x)`
What is the purpose of the DISTINCT keyword in aggregation functions?
What is the purpose of the DISTINCT keyword in aggregation functions?
Which of the following correctly describes how aggregation functions operate?
Which of the following correctly describes how aggregation functions operate?
Flashcards
Aggregation Function
Aggregation Function
Calculates a single numerical value from multiple rows for a given attribute.
COUNT(*) function
COUNT(*) function
Counts the number of tuples in a result set.
COUNT(DISTINCT attribute) function
COUNT(DISTINCT attribute) function
Counts the number of unique values in a specified attribute.
MIN(attribute) function
MIN(attribute) function
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AVG(attribute) function
AVG(attribute) function
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Study Notes
Aggregation Functions
- Aggregation functions calculate a single value from multiple tuples for a specific attribute.
- Examples include calculating the sum of project budgets or finding the minimum value in an attribute.
- The
COUNTfunction counts tuples based on specified attributes.DISTINCToption eliminates duplicate counts.
MIN(x),MAX(x),AVG(x), andSUM(x)find the minimum, maximum, average, and sum of values in attributex, respectively.- Aggregation functions operate on data within a
SELECTclause, never aWHEREclause.
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