SQL Server/T-SQL/Constraints/Constraints Basics

Enable a column to optionally not require a value by designating it as a nullable column

1> -- Nullability
2>
3> -- Enable a column to optionally not require a value by designating it as a
4> -- nullable column.
5>
6> CREATE TABLE MyTable
7>      ( Category nVarChar(50) NOT NULL
8>      , MyDescription nVarChar(50)
9> )
10> INSERT MyTable (Category) VALUES ("Category1")
11>
12> SELECT * FROM MyTable
13> GO
(1 rows affected)
Category                                           MyDescription
-------------------------------------------------- -------------------------------
Category1                                          NULL
(1 rows affected)
1>
2> drop table MyTable
3> GO
1>

NOT NULL column and NULL column

1> CREATE TABLE MyTable
2>      ( Category nVarChar(50) NOT NULL
3>    , MyDescription nVarChar(50) NULL
4> )
5>
6>
7> INSERT MyTable (Category) VALUES ("Category1")
8>
9> SELECT * FROM MyTable
10> GO
(1 rows affected)
Category                                           MyDescription
-------------------------------------------------- -----------------
Category1                                          NULL
(1 rows affected)
1>
2> drop table MyTable
3> GO
1>