• Null represents absence of data value of a column in a row
• Null is a SQL keyword
• Null is neither a data type no characteristic of data
• When doing is ascending sorting Null is before numeric negative values and before blank character values
• To prohibit nulls columns have to be defined as Not Null
• Null on arithmetic operations always produces Null result
• It is possible to use Null and not Null in select statement

Example

Select customer_id, address

From   basic_data

Where address is not null