NULL vs NOT NULL [closed]

Answer 1

When a field is set to NOT NULL, it cannot be empty. Which means you have to specify a value for that field when inserting a record.

Answer 2

Just to clarify your pointÖ Empty strings are not being set to NULL in any database that conforms to the ANSI standard for SQL. NULLs are not the same as empty strings. Columns given an explicit NULL value or no value are assigned NULL.

Here are a couple of advantages of not using NULLs. You save the space for the bit used to differentiate the NULL value. You also make the meaning of statements, such as "field <> value" more clear. Also, some databases have trouble optimizing statements such as "coalesce(field, '') <> value" to use an index.

Sometimes, NULLs are needed, particularly when you are inserting incomplete records. And, because by default columns allow NULLs, laziness ensures that almost all columns in all databases do accept NULL values.

Answer 3

NOT NULL obligate to specify particular value for the field.

use NULL when you need to keep empty values for the field.

use NOT NULL when you want forbid empty values for the field. Additional goal that the most DBs works slowly with NULL-values. So if you doubt use NOT NULL.

Answer 4

NOT NULL is a constraint which ensures there is a value in the column for every row. This is good practice when applied correctly because you have to be careful with null values in tables when doing operations like joins because no null is equal to any other null

http://en.wikipedia.org/wiki/Null_(SQL)

Answer 5

If you need to represent unknown data in a column, you make it nullable. If you will always have data in the column, it's better to make it not nullable, as

1. Dealing with nulls can be annoying and counterintuitive
2. It saves a bit of space
3. On some database systems, null values are not indexed.