(Not) Using `nvarchar(max)` in SQL Server and Azure SQL Databases

When working with SQL Server and Azure SQL Database, one data type you’ll often come across is nvarchar(max). This type is designed for storing variable-length Unicode data, which can be helpful when handling text that varies widely in size.

nvarchar(max) can store up to 2³¹-1 characters, roughly 2 GB of data. This makes it suitable for storing large text blocks like user comments, blog posts, or documents. It supports a wide range of characters, making it useful for multi-language applications.

However, while nvarchar(max) offers flexibility, it comes with significant downsides, primarily in terms of memory usage. Using nvarchar(max) can lead to substantial memory consumption, as it allows for very large amounts of data, whether or not you actually need such capacity. This can affect performance, especially if the data you’re storing is smaller or more predictable in size. Operations involving sorting, indexing, and retrieving large volumes of text can be slower and less efficient.

For most applications, it’s better to avoid nvarchar(max) unless absolutely necessary. Instead, consider using nvarchar(n), where “n” specifies the maximum number of characters you expect to store. This approach helps conserve memory and improves performance by avoiding the overhead associated with very large data fields. Also, be cautious with indexing on large text columns. If you need search capabilities, look into full-text indexing or using computed columns to handle large text more efficiently.

So, while nvarchar(max) provides flexibility, its high memory usage and potential performance issues make it less ideal for many scenarios. By choosing more appropriately sized data types and indexing strategies, you can ensure your database remains efficient and responsive.

Here’s a small query that can be used to identify all columns that are using nvarchar(max) type in your database:

USE [databaseName]
GO

SELECT TABLE_SCHEMA
	,TABLE_NAME
	,COLUMN_NAME
	,DATA_TYPE
	,CHARACTER_MAXIMUM_LENGTH
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATA_TYPE = 'nvarchar'
	AND CHARACTER_MAXIMUM_LENGTH = - 1;

Then after getting the results you can choose the best action for each one. Also note that it can be done for other types, just like varchar(max), and other databases, just like MySQL, PostgreSQL or Oracle. Be careful!

Peace ✌️