How many rows in the following SELECT statement will return a null prerequisite? SELECT prerequisite, COUNT(*)...
How many rows in the following SELECT statement will return a null prerequisite?
SELECT prerequisite, COUNT(*)
FROM course
WHERE prerequisite IS NULL
GROUP BY prerequisite;
|
None |
||
|
One |
||
|
Multiple |
Homework Answers
Answer
One
Explanation :
As we are retrieving prerequisite from the table course by grouping it by prerequisite, it will group all the null prerequisite together in to a single row and only one row will be returned. So, only one row in the above SELECT statement will return a null prerequisite.
Group by command groups all the rows having same values in to a single row. In the same way, all the rows having null values are grouped together in a single row.
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How many rows in the following SELECT statement will return a
null prerequisite?
SELECT prerequisite, COUNT(*)...
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