What are the Limits and Behaviors of VARCHAR and NVARCHAR in SQL Server?

Understanding SQL Server's VARCHAR and NVARCHAR Data Types

SQL Server utilizes two key string data types: VARCHAR and NVARCHAR. Knowing their limitations is crucial for effective database design and preventing data loss through truncation.

NVARCHAR and VARCHAR Size Limits:

• NVARCHAR: Stores Unicode characters. The default maximum length is 4000 characters (NVARCHAR(4000)). However, using NVARCHAR(MAX) allows for storage of up to 2GB of Unicode data.

• VARCHAR: Stores single-byte characters. The default maximum length is 8000 characters (VARCHAR(8000)). Similarly, VARCHAR(MAX) supports up to 2GB of single-byte data.

String Concatenation and Data Type Implications

The outcome of string concatenation depends heavily on the input data types:

• VARCHAR(n) VARCHAR(n): Results in a VARCHAR(8000), capped at 8000 characters.
• NVARCHAR(n) NVARCHAR(n): Results in an NVARCHAR(4000), capped at 4000 characters.
• VARCHAR(n) NVARCHAR(n): Defaults to NVARCHAR(4000) due to NVARCHAR's higher precedence.

Importantly, using NVARCHAR(MAX) or VARCHAR(MAX) avoids truncation during concatenation, provided the combined length remains under the 2GB limit.

String Literal Data Types

• Literals prefixed with N (e.g., N'My String') are treated as NVARCHAR(n) (up to 4000 characters) or NVARCHAR(MAX) (if exceeding 4000 characters).
• Literals without the N prefix (e.g., 'My String') are treated as VARCHAR(n) (up to 8000 characters) or VARCHAR(MAX) (if exceeding 8000 characters).

Working with Extensive SQL Queries

Utilizing the CONCAT Function:

The CONCAT function is recommended for large string concatenations because it treats all inputs as MAX data types, preventing truncation.

Avoiding the = Operator:

When appending strings, avoid the = operator with non-MAX data type variables, as this can lead to truncation. Instead, directly assign the concatenated result to the variable.

Displaying Large Queries in Management Studio

To view lengthy dynamic SQL queries without truncation in SQL Server Management Studio:

1. Set the "Results to Grid" mode.
2. Execute the following query, replacing @SQL with your dynamic SQL variable:

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

This XML-based approach allows for viewing strings of virtually unlimited length.

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