Nulls Flashcards
1
Q
What is a NULL?
A
An all purpose marker to represent incomplete information
2
Q
NULL are the main source of ________ and ________________
A
problems, inconsistencies
3
Q
What are four meanings of NULL?
A
- Missing value
- N/A
- Constant
- Unknown
4
Q
We can use ______ to give NULL values more meaning in our DB
A
CHECKs
5
Q
NULL is not allows in ________ keys
A
primary
6
Q
Every _______ operation that involves a NULL results in NULL. NULL is treated is a __________(undefined)
A
arithmetic, non-applicable
7
Q
Aggregate functions ignore _____ except for ______
A
NULLs, COUNT
8
Q
NULL is treated like any other value in ___ operations
A
set
9
Q
In selection condition, a NULL in a condition results in _____ tuple
A
empty
10
Q
In comparisons, NULL has truth value ______
A
unknown
11
Q
Marked NULLs allows ______ ________ of missing values
A
cross referencing
