NVL for SQL Server

Hey Dev, are you looking for a reliable function to handle NULL values in your SQL Server database? Look no further than NVL. This simple yet powerful function has been a staple in Oracle databases for years and now it’s available for SQL Server users too. In this article, we’ll dive deep into the NVL function and explore its many use cases.

What is the NVL Function?

The NVL function is used to handle NULL values in SQL. It takes two arguments: the first is the value to check for NULL, and the second is the value to return if the first argument is NULL. For example, if you wanted to return the string “Unknown” if a column called “status” had a NULL value, you would use the NVL function like this:

Code
Result
NVL(status, ‘Unknown’)
Unknown

As you can see, the NVL function returns the second argument if the first argument is NULL. If the first argument is not NULL, the function returns the first argument.

Using NVL with Numbers

One common use case for the NVL function is with numbers. If you’re working with a numeric column that could contain NULL values, you may want to replace those NULLs with a default value. Here’s an example:

Code
Result
NVL(price, 0)
0

In this example, if the “price” column is NULL, the NVL function returns 0. If it’s not NULL, the function returns the value of the “price” column.

Using NVL with Dates

You can also use NVL with dates. If you have a date column that could contain NULL values, you may want to replace those NULLs with a default date. Here’s an example:

Code
Result
NVL(start_date, ’01/01/2000′)
01/01/2000

In this example, if the “start_date” column is NULL, the NVL function returns January 1st, 2000. If it’s not NULL, the function returns the value of the “start_date” column.

Using NVL with Strings

NVL can also be used with strings. If you have a string column that could contain NULL values, you may want to replace those NULLs with a default string. Here’s an example:

Code
Result
NVL(name, ‘Unknown’)
Unknown

In this example, if the “name” column is NULL, the NVL function returns “Unknown”. If it’s not NULL, the function returns the value of the “name” column.

Using NVL with Multiple Columns

You can also use NVL with multiple columns. If you have two columns that could contain NULL values and you want to choose one of them as the default value, you can use NVL like this:

Code
Result
NVL(first_name, last_name)
last_name if first_name is NULL, otherwise first_name

In this example, if the “first_name” column is NULL, the NVL function returns the value of the “last_name” column. If “first_name” is not NULL, the function returns the value of the “first_name” column.

Using NVL in Where Clauses

NVL can also be used in WHERE clauses to filter out NULL values. For example, if you wanted to select all rows where the “status” column is not NULL, you could use this code:

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Code
Result
SELECT * FROM my_table WHERE NVL(status, ‘Unknown’) != ‘Unknown’
Selects all rows where the “status” column is not NULL

In this example, the NVL function is used to replace NULL values with the string “Unknown”. The WHERE clause then filters out any rows where the “status” column is equal to “Unknown”.

Using NVL in Views

You can also use NVL in views to simplify your queries. For example, if you have a view that contains a column with NULL values, you can use NVL to replace those NULLs with a default value. Here’s an example:

Code
Result
CREATE VIEW my_view AS SELECT NVL(price, 0) AS price FROM my_table
Creates a view that replaces NULL values in the “price” column with 0

In this example, the NVL function is used to replace NULL values in the “price” column with 0. The resulting view, “my_view”, will always return a value for the “price” column, even if the original value was NULL.

Using NVL in Stored Procedures

Finally, you can use NVL in stored procedures to handle NULL values. For example, if you have a stored procedure that accepts a parameter that could be NULL, you can use NVL to replace that NULL value with a default value. Here’s an example:

Code
Result
CREATE PROCEDURE my_proc(@status VARCHAR(50)) AS BEGIN SELECT * FROM my_table WHERE NVL(status, ‘Unknown’) = @status END
Creates a stored procedure that replaces NULL values in the “status” parameter with “Unknown”

In this example, the NVL function is used to replace NULL values in the “status” parameter with the string “Unknown”. This ensures that the stored procedure will always have a value to work with, even if the parameter is NULL.

FAQ

What’s the difference between NVL and COALESCE?

COALESCE is similar to NVL in that it handles NULL values, but it can take any number of arguments. It returns the first non-NULL value in the list of arguments. NVL, on the other hand, only takes two arguments and returns the second argument if the first argument is NULL.

Can NVL be used with VARCHAR(MAX) columns?

Yes, NVL can be used with VARCHAR(MAX) columns just like any other data type.

What happens if both arguments to NVL are NULL?

If both arguments to NVL are NULL, the function will return NULL.

Can NVL be used with other database systems besides SQL Server and Oracle?

No, NVL is specific to SQL Server and Oracle databases. Other database systems may have similar functions with different names.

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