databases Online Quiz - 111
|Description: databases Online Quiz - 111
|Number of Questions: 20
|Created by: Aliensbrain Bot
What is true of using group functions on columns that contain NULL Values
To answer this question, the user needs to understand the behavior of group functions when used on columns that contain NULL values.
Option A is correct. Group functions ignore NULL values in columns. For example, the AVG function calculates the average of all non-NULL values, while the COUNT function counts all non-NULL values. This means that NULL values are not included in the calculation and do not affect the result.
Option B and Option C are incorrect because they describe the behavior of specific group functions, rather than the behavior of group functions in general. The behavior of each group function depends on the specific function being used and the data type of the column being aggregated.
Option D is incorrect because group functions can be accurately used on columns that contain NULL values. However, it is important to keep in mind that NULL values may affect the result of certain operations, such as the SUM function. If a column contains both NULL and non-NULL values, the SUM function will return a NULL value, unless the column is aggregated using the NVL function or a similar function that replaces NULL values with a default value.
Therefore, the correct answer is:
The Answer is: A. Group functions on columns ignore NULL values.
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What does the following SQL statement do: SELECT Customer, COUNT(Order) FROM Sales GROUP BY Customer HAVING COUNT(Order) >5
To understand this SQL statement, the user needs to know the basic structure of SQL queries. In this case, the statement selects two fields, Customer and COUNT(Order), from the Sales table. It then groups these fields by Customer and applies a filter using the HAVING clause to only return rows where the count of orders for that customer is greater than 5.
A. This option is incorrect because the statement is not selecting the total number of orders, but rather the count of orders for each customer.
B. This option is correct. The statement is selecting all customers from the Sales table that have made more than 5 orders.
C. This option is incorrect because the statement is not selecting all customers, but rather only those who have made more than 5 orders.
D. This option is incorrect because option B is correct.
Therefore, the answer is: B. Selects all customers from table Sales that have made more than 5 orders.