MySQL Programming Question: Download Questions PDF
What Are NULL Values?
Answer:
NULL is a special value that represents no value. Here are basic rules about NULL values:
► NULL presents no value.
► NULL is not the same as an empty string ''.
► NULL is not the same as a zero value 0.
► NULL can be used as any data type.
► NULL should not be used in any comparison options.
► NULL has its own equality operator "IS".
► NULL has its own not-equality operator "IS NOT".
The tutorial exercise shows you some interesting examples:
SELECT 0 IS NULL FROM DUAL;
0
SELECT 0 IS NOT NULL FROM DUAL;
1
SELECT '' IS NULL FROM DUAL;
0
SELECT '' IS NOT NULL FROM DUAL;
1
SELECT NULL IS NULL FROM DUAL;
1
SELECT NULL IS NOT NULL FROM DUAL;
0
► NULL presents no value.
► NULL is not the same as an empty string ''.
► NULL is not the same as a zero value 0.
► NULL can be used as any data type.
► NULL should not be used in any comparison options.
► NULL has its own equality operator "IS".
► NULL has its own not-equality operator "IS NOT".
The tutorial exercise shows you some interesting examples:
SELECT 0 IS NULL FROM DUAL;
0
SELECT 0 IS NOT NULL FROM DUAL;
1
SELECT '' IS NULL FROM DUAL;
0
SELECT '' IS NOT NULL FROM DUAL;
1
SELECT NULL IS NULL FROM DUAL;
1
SELECT NULL IS NOT NULL FROM DUAL;
0
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