What difficulties can arise when applying an index on a column of type NVARCHAR(MAX)?

The NVARCHAR(MAX) type column is designed to store very large strings (up to 2 GB of data). When attempting to create an index on such a column, the following difficulties arise:

• Index size limitations: SQL Server indexes have a key size limit (for example, 900 bytes). NVARCHAR(MAX) values can be much longer, so a full index on the entire column length is impossible.
• Indexing only the first N characters: Often, an index is created with a prefix (e.g., the first 450 characters), which reduces search efficiency for the full value.
• Performance: Indexing large text fields requires additional resources and can slow down insert and update operations.
• Full-Text Search: For full-text search on such columns, it is better to use full-text indexes rather than regular indexes.

Example of creating a prefix index:

CREATE INDEX IX_Table_Column ON TableName(ColumnName(450));

Thus, when working with NVARCHAR(MAX), it is important to consider these limitations and choose the appropriate index type depending on the task.