Null / Not Null value
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A NULL value in a database represents a field with no value, which is different than a field containing a zero or spaces. To test for NULL values, the IS NULL and IS NOT NULL operators must be used instead of comparison operators. The IS NULL operator selects records where the column is empty/NULL, while IS NOT NULL selects records where the column contains a non-empty value. For example, to find employee names where the salary field is empty, use "SELECT names FROM Employee WHERE Salary IS NULL".
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Null / Not Null value
- 1. By : Dhirendra Chauhan
- 2. NULL Value “A field with a NULL value is a field with no value.” “A NULL value is different from a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation!”
- 3. How to Test for NULL Values? It is not possible to test for NULL values with comparison operators, such as =, <, or <>. We will have to use the IS NULL and IS NOT NULL operators instead.
- 4. IS NULL Syntax: SELECT column_names FROM table_name WHERE column_name IS NULL; The IS NULL operator is used to test for empty values (NULL values). Example: SELECT names FROM Employee WHERE Salary IS NULL; Always use IS NULL to look for NULL values.
- 5. IS NOT NULL Syntax: SELECT column_names FROM table_name WHERE column_name IS NOT NULL; The IS NOT NULL operator is used to test for Non- empty values (For values). Example: SELECT names FROM Employee WHERE Salary IS NOT NULL;
- 6. THANK YOU