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What is a column?
A column is a vertical entity in a table that contains all information associated with a
specific field in a table.
For example, a column in the CUSTOMERS table is ADDRESS, which represents location
description and would be as shown below:
+-----------+
| ADDRESS |
+-----------+
| Ahmedabad |
| Delhi |
| Kota |
| Mumbai |
| Bhopal |
| MP |
| Indore |
+----+------+
What is a NULL value?
A NULL value in a table is a value in a field that appears to be blank, which means a field
with a NULL value is a field with no value.
It is very important to understand that a NULL value is different than a zero value or a
field that contains spaces. A field with a NULL value is the one that has been left blank
during a record creation.
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