Why is my NVARCHAR(MAX) variable being truncated in SQL Server dynamic SQL?

Understanding the Truncation Issue with NVARCHAR(MAX)

When creating dynamic SQL queries, it's crucial to ensure that string concatenation operations do not result in unexpected truncation. In this scenario, the issue faced with @Query being truncated to 4000 characters despite its NVARCHAR(MAX) data type warrants investigation.

Implicit Conversion Woes

The culprit lies in implicit conversion. When concatenating strings containing Unicode/nChar/nVarChar values, SQL Server automatically converts them to the more restrictive data type nVarChar(4000). This conversion is performed before any explicit conversion to NVARCHAR(MAX) assigned to the variable @Query.

A Simple Solution to Avoid Truncation

The remedy is to explicitly force the conversion to nVarChar(MAX) before any concatenation operations. By initializing @Query with CAST('' as nVarChar(MAX)), the subsequent concatenation operations will append to a string that is already defined as maximum capacity, preventing truncation.

Overcoming 8000 Character Limit

If the maximum limit is 8000 characters, it indicates a conversion to VarChar(8000) due to the absence of Unicode data. Similarly, explicit type casting can be employed to force the conversion to nVarChar(MAX).

Literal String Constraints

It's important to note that even with NVARCHAR(MAX), a single uninterrupted literal string cannot exceed 4000 (or 8000 for VarChar) characters. To avoid truncation, such strings should be broken up using concatenation.

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