What is the meaning of the prefix N in T-SQL statements and when should I use it?

Prime use cases for the N prefix

Deploy the N prefix:

• For NCHAR, NVARCHAR, and NTEXT data types.
• To correctly represent characters outside the ASCII range.
• When working with columns holding Unicode data, particularly when the default collation does not support the languages in question.

Neglecting to use the N prefix can lead to:

• Data corruption: Non-ASCII characters may be misconverted or lost.
• Incorrect Unicode data: Resulting in failed or misplaced queries.
• Performance degradation: Caused by implicit conversion and the possible inefficiency of the execution plan.

Not just a prefix, a data safeguard

The N prefix isn't just a character, it's a crucial safeguard for data:

• Unicode preservation: Prevents misinterpretation of data by mapping it to the default code page.
• Index efficiency: Ensures nchar/nvarchar fields utilize their indexes properly, enhancing retrieval speed.
• Protection against implicit conversions: Helps avoid conversion from non-Unicode to Unicode data types, reducing operational inefficiency.

Dodging common miscues

When leveraging the N prefix in T-SQL, be wary of:

• Ignoring collation: Verify collation settings support the Unicode characters you plan to accommodate.
• Mismatching data types: Data types of N prefixed literals should match with the columns to thwart conversion issues.
• Overuse with non-Unicode fields: Applying the N prefix to varchar fields unnecessarily can lead to performance bottlenecks and bewilderment.

Deciphering the role of default code pages

Unraveling code pages:

• Default code page: Usually derived from the SQL server’s installation language or region settings.
• Character identification: Non-ASCII characters risk misrecognition unless the N prefix is used.
• Risk of data mismatch: Absence of prefix could lead to a Unicode string incorrectly represented in the database.