What are the Character Limits and Truncation Rules for NVARCHAR and VARCHAR in SQL Server?

SQL Server's NVARCHAR and VARCHAR: Character Limits and Truncation Behavior

Contrary to popular assumptions, NVARCHAR(MAX) in SQL Server can handle significantly more data than 4000 characters—up to 2GB (or even more in SQL Server 2008 and later). However, NVARCHAR(n), where 'n' represents a specific number, is limited to a maximum of 4000 characters.

Understanding Potential Truncation Issues

String concatenation can lead to unexpected truncation depending on the data types involved:

• VARCHAR(n) VARCHAR(n): Truncation occurs at 8000 characters.
• NVARCHAR(n) NVARCHAR(n): Truncation at 4000 characters.
• VARCHAR(n) NVARCHAR(n): Truncation at 4000 characters (resulting in an NVARCHAR(4000) data type).
• [N]VARCHAR(MAX) [N]VARCHAR(MAX): No truncation for data under the 2GB limit.
• VARCHAR(MAX) VARCHAR(n) or VARCHAR(MAX) NVARCHAR(n): No truncation under the 2GB limit (resulting in VARCHAR(MAX)).
• NVARCHAR(MAX) VARCHAR(n): The VARCHAR(n) input is implicitly cast to NVARCHAR(n) before concatenation. Truncation happens if VARCHAR(n) exceeds 4000 characters.

String Literal Data Type Considerations

• String literals beginning with 'N' are treated as NVARCHAR(n), with 'n' being the string's length (up to 4000). Longer literals become NVARCHAR(MAX).
• Unprefixed string literals become VARCHAR(n) (where 'n' equals the string length) for strings shorter than 8000 characters; otherwise, they're treated as VARCHAR(MAX).

Best Practices and Solutions

• Utilize the CONCAT Function: The CONCAT function simplifies concatenation of multiple arguments, supporting MAX data types and preventing intermediate truncation problems.
• Exercise Caution with =: Using = for variable assignments can cause truncation with non-MAX data types. Use it cautiously.
• Prevent Truncation: For strings in the 4001-8000 character range, always prefix string literals with 'N'. Start concatenations with NVARCHAR(MAX) to avoid automatic truncation.

Viewing Extended Queries Without Truncation in SSMS

To view long queries exceeding the 4000-character limit in SQL Server Management Studio (SSMS) grid view, use this technique:

<code class="language-sql">SELECT @SQL AS [processing-instruction(x)] FOR XML PATH</code>

This method effectively bypasses the SSMS grid view's 4000-character limitation.

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