SQL Not Null Constraint-Checking If a Field in a Table is Not Empty

When you set up a database, you will always want certain fields to be filled out in a table. But the user must remember to fill or willfully fill those particular fields. Certain checks or constraints must be incorporated into fields that require data to avoid such issues. The user would be compelled to enter data in those fields where it is required. We refer to this as a Not Null Constraints in SQL.The following paragraphs will teach us about various aspects of these SQL Server Not Null constraints in the following paragraphs.

What are SQL Not Null Constraints?

A column can hold NULL values by default.A column cannot accept null values because of the NOT NULL in SQL.Because this makes a field have to have a value at all times, you can't add a value to it when you add a new record or update an existing one.

Properties of MS SQL Not Null Constraint

Following are the properties of Not Null Constraint in SQL Server

•  It ensures that a column cannot store a NULL value.
•  A column cannot store a null value if marked as NOT NULL.

Advantages of SQL Not Null Constraint

Following are the advantages of not having null constraints in SQL Server

1. Since Not Null fields don't need a Null variable, it saves space if the column is short (like 1 character) and mainly contains values.
2. When coding in an application program, you don't have to worry about null values or write additional code for the null indicator (as opposed to COBOL).
3. The fields must have a value, such as a "Y"/"N" situation. Use Not Null to compel people to respond to a Yes/No question.
4. When writing queries, you are not required to include phrases such as "Where col > 'Y' and col IS NOT NULL." As a result, the query size shrinks.
5. You shouldn't be concerned about the Joined column having a null value when joining tables.
6. It might also be helpful in aggregate functions, especially if you want an int column's default value to be "1."
7. Since null values are not checked for RI, it also helps ensure relational integrity.

Disadvantages of SQL Not Null Constraint

Following are the disadvantages of SQL Not a Null Constraint

1. Contrary to the first point, if you have a large field and use Not Null, you might be wasting space if you don't want that field to be populated most of the time.
2. You must ensure that you pass a value for a Not Null column when inserting rows.
3. You must choose that column's values (or defaults) beforehand.
4. Using Null, you can smartly use Null values without writing much code. For example, if there is a frequency of "Monthly" and "Yearly" and you want to add a new frequency of "Semi-monthly," you don't have to fill that column with an "S" if NULLs are allowed. If it shows null, you will get to know that it is semi-monthly. You can introduce a new frequency with impunity. Your program can deal with that Null. If a column is not null, this cannot be done.
5. While a Null can remain a Null, you must modify that Not Null value if your application's requirements change.

Implementing not null constraint in SQL table

The below SQL makes sure that the "ID", "LastName", and "FirstName" columns will NOT accept NULL values when the "Persons" table is formed:

CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);

The output is as follows

MySQL Not Null constraint in Alter Table

To develop a NOT NULL constraint on the "Age" column when the "Persons" table already exists, use the following SQL:

ALTER TABLE Persons
ALTER COLUMN Age int NOT NULL;

Implementation of SQL Not Null Constraint using SQL Server Management Studio

We can implement MSSQL Not null constraint using SQL Server Management Studio. The steps are as follows

1) Log in to SQL Server Management Studio.

2) Select The Database and Table, Right-Click, and Select a Design.

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Conclusion

In the above few paragraphs, we learned about Not Null Constraint in SQL Server. We discussed its usage, advantage, and disadvantages. We also learned how to implement the Not Null constraint in a table. This can be a starting point for people who want to learn about SQL Server Not Null Constraints.