Why We Use Not Null In Sql

SQL NOT NULL Constraint. By default, a column can hold NULL values. The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.

Alternatively, the NOT NULL constraint can be added to an existing table using the ALTER TABLE statement ALTER TABLE table_name MODIFY column_name data_type NOT NULL Defining a Nullable Column. Many RDBMSs allow us to explicitly define a column as nullable by using NULL without the NOT. In this case, we simply omit the NOT from the above

Using IS NULL or IS NOT NULL in WHILE. A T-SQL program is able to check for NULL or NOT NULL values in the argument at the top of a WHILE loop. Here is an example using IS NULL in a WHILE loop. This code is not based on a real table and is just for illustrative purposes.

SQL NOT NULL on ALTER Table. We can also add a NOT NULL constraint in the existing table using the ALTER statement. For example, if the EMPLOYEES table has already been created then add NOT NULL constraints to the quotNamequot column using ALTER statements in SQL as follows Query ALTER TABLE Emp modify Name Varchar50 NOT NULL

So, to check for values that aren't NULL we use IS NOT NULL. NULL with IN and EXISTS. There are two similar operators in SQL that let you check for a range of values IN and EXISTS. The IN keyword can use a set of values or a subquery. EXISTS is used with a subquery. Both of these keywords can have the NOT keyword used with them NOT IN and NOT

Why Use NULL Values? What situations call for a NULL value? Perhaps we don't know the value when we create a record. For example, suppose we have the table person with the column birth_date.We need to create a new record, but we don't know the person's birth_date yet. So, we can put a NULL value into the column birth_date and enter the actual value when we get it.

In this example, both quotemployee_idquot and quotfirst_namequot columns are required to have non-null values for every row. Use cases. Enforce Data Integrity To guarantee that specific columns contain valid and non-null data, preventing missing or unknown information in critical fields. Ensure Data Quality To improve data accuracy by requiring that essential information is provided for every row

By default, a column can contain NULL values. So, to allow NULL values for a column we do not really have to do anything though it is possible to explicitly specify the same using the NULL constraint. But if we do not want a column to have NULL value it has to be explicitly specified using the NOT NULL constraint.

The SQL IS NOT NULL Operator. Let's start with the basics. In SQL, NULL is a special value or rather, a lack of value that represents missing or unknown information. It's like when you're filling out a form and leave a field blank - that's essentially what NULL is in a database. We can also use IS NOT NULL in more complex UPDATE statements

For instance, we have a person table, lastname is not allowed to be null. There is no default lastname we could assign though, if the person doesn't have a name, the record doesn't get created. On the other hand, you might have a DateCreated field with a default value of the current date.