VARCHAR vs NVARCHAR: Complete Database Guide

The main difference between varchar and nvarchar is that nvarchar supports Unicode characters while varchar is limited to ASCII/Latin characters, but there are significant additional differences in storage requirements, performance implications, and collation behavior that make varchar preferable in many scenarios beyond just storage concerns.

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Contents

• Character Encoding and Unicode Support
• Storage Requirements
• Performance Considerations
• Collation Differences
• When to Use Each Data Type
• Modern Considerations and Best Practices
• Practical Examples and Recommendations

Character Encoding and Unicode Support

The fundamental difference between varchar and nvarchar lies in their character encoding capabilities. Varchar uses single-byte encoding and can store up to 8,000 characters, limited to the ASCII character set (0-255) and any specific character set defined by the column’s collation. In contrast, nvarchar uses Unicode encoding (UTF-16 in SQL Server) and can store up to 4,000 characters, supporting the full Unicode character set including multibyte characters.

“If you store character data that reflects multiple languages in SQL Server (SQL Server 2005 and later), use Unicode data types (nchar, nvarchar, and ntext) instead of non-Unicode data types (char, varchar, and text).” - Microsoft Learn

This Unicode support is crucial for:

• International applications requiring Arabic, Chinese, Russian, or other non-Latin scripts
• Modern applications that need to store emojis, special symbols, or mathematical notations
• Email addresses and URLs which can now contain Unicode characters

However, this Unicode support comes with additional complexity in how characters are stored and processed, particularly in higher Unicode ranges (65,536-1,114,111) where one character may use two byte-pairs in nvarchar.

Storage Requirements

Storage efficiency is one of the most significant practical differences between these data types:

“For example, VARCHAR(100) can store up to 100 non-Unicode characters, which equates to a maximum storage size of 100 bytes (100 characters * 1 byte per character).” - The DBA Hub

This doubling of storage requirements has several practical implications:

• Row size limitations: You may need shorter nvarchar columns to keep rows within the 8,060 byte row limit or 8,000 byte character column limit
• nvarchar(max) limitations: Since nvarchar uses two bytes per character, nvarchar(max) can store up to approximately half the number of characters compared to varchar(max)
• Database size impact: Applications using nvarchar will require approximately double the storage space for character data

Performance Considerations

While storage is obvious, the performance differences are more subtle but equally important:

Memory and Processing Impact
“Disk space is not the issue… but memory and performance will be. Double the page reads, double index size, strange LIKE and = constant behaviour etc.” - Stack Overflow

Key performance differences include:

1. Page reads: nvarchar requires double the page reads for the same amount of character data
2. Index size: Indexes on nvarchar columns are larger, potentially impacting query performance
3. String operations: LIKE operations and equality comparisons behave differently
4. Encoding conversions: “By using nvarchar rather than varchar, you can avoid doing encoding conversions every time you read from or write to the database. Conversions take time, and are prone to errors.” - Stack Overflow

Performance Optimization
“VARCHAR can be more performant in terms of storage and query processing for non-Unicode data since it consumes less space and requires fewer bytes to be processed.” - TSQL.info

The performance difference may not be significant in most cases, but it becomes noticeable in:

• High-concurrency environments
• Large-scale operations involving string manipulations
• Systems with limited memory resources
• Applications requiring frequent string comparisons

Collation Differences

Collation behavior differs significantly between varchar and nvarchar:

VARCHAR Collation

• Uses specific character set collations (e.g., Latin1_General_100_BIN2)
• Sorts and compares characters based on the defined collation rules
• Can use binary collations for case-sensitive comparisons

NVARCHAR Collation

• “NVARCHAR is collation-sensitive, meaning that the collation settings of the…” - The DBA Hub
• Uses Windows collation rules for sorting
• Generally has consistent sorting behavior across SQL and Windows collations
• No difference in sorting behavior for SQL and Windows collations when using Unicode data types

This collation difference can affect:

• Query results when using ORDER BY clauses
• String comparison operations
• Search functionality in international applications

When to Use Each Data Type

Use VARCHAR when:

• You are only using ASCII characters (A-Z, 0-9, basic punctuation)
• Storage efficiency and performance are critical
• Working with legacy systems where ASCII is the standard
• Storing data like postal codes, product codes, or identifiers that won’t contain non-ASCII characters
• “If storing postal codes (i.e. zip codes), use VARCHAR since it is an international standard to never use any letter outside of A-Z.” - Stack Overflow

Use NVARCHAR when:

• You need to store text in multiple languages
• Your application requires support for emojis or special characters
• Storing email addresses and/or URLs which can contain Unicode characters
• Future-proofing your application for international expansion
• Working with modern applications that might need to handle diverse character sets

“Choose VARCHAR when you are certain that your data will only contain ASCII characters. However, if you are only using… compression and the data isn’t off-row. But without row compression, nvarchar uses double the length compared to varchar.” - Microsoft Q&A

Modern Considerations and Best Practices

SQL Server 2019 and UTF-8 Support
Starting with SQL Server 2019, you have additional options:

“For example, changing an existing column data type with ASCII strings from NCHAR(10) to CHAR(10) using an UTF-8 enabled collation, translates into nearly 50% reduction in storage requirements.” - Database Administrators Stack Exchange

UTF-8 enabled collations allow you to:

• Store Unicode data in varchar and char columns
• Achieve storage efficiency similar to varchar while maintaining Unicode support
• Reduce character conversion overhead
• “Starting with SQL Server 2019 (15.x), consider using a UTF-8 enabled collation to support Unicode and minimize character conversion issues.” - Microsoft Q&A

Best Practices

1. Default to NVARCHAR for new applications that might need internationalization
2. Use VARCHAR only when you’re certain about the character requirements
3. Consider UTF-8 collations in SQL Server 2019+ for optimal storage/performance balance
4. Review existing schemas to determine if varchar could be safely converted to nvarchar or vice versa
5. Test performance with your specific workload before making final decisions

Practical Examples and Recommendations

Example 1: User Authentication System

• Email field: Use NVARCHAR - emails can contain Unicode characters and international domains
• Username field: Use VARCHAR if usernames are ASCII-only, NVARCHAR if international usernames are supported
• Password field: Use VARCHAR - passwords are typically ASCII

Example 2: E-commerce Product Catalog

• Product name: Use NVARCHAR - product names may contain international characters
• SKU/Barcode: Use VARCHAR - typically alphanumeric ASCII codes
• Description: Use NVARCHAR - may contain technical symbols or international terms

Example 3: Financial System

• Account numbers: Use VARCHAR - typically numeric or simple alphanumeric
• Transaction notes: Use NVARCHAR - may contain international merchant names or symbols
• Customer names: Use NVARCHAR - international customer base

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Sources

1. What is the difference between varchar and nvarchar? - Stack Overflow
2. varchar vs nvarchar - Microsoft Q&A
3. Write differences between varchar and nvarchar - Database Administrators Stack Exchange
4. Difference between VARCHAR and NVARCHAR in SQL Server | Java67
5. Collation and Unicode Support - SQL Server | Microsoft Learn
6. Understanding the Difference Between nVARCHAR and VARCHAR - The DBA Hub
7. What are the main performance differences between varchar and nvarchar SQL Server data types? - Stack Overflow
8. Difference Between VARCHAR and NVARCHAR: A Comprehensive Guide | Medium
9. Difference between Varchar and Nvarchar in sql - TSQL.info
10. When nvarchar/nchar is going to be used with SQL Server 2019? - Database Administrators Stack Exchange

Conclusion

The difference between varchar and nvarchar extends far beyond just multibyte character support. While nvarchar is essential for international applications requiring Unicode characters, varchar offers significant advantages in storage efficiency, performance, and simplicity for ASCII-only data.

Key considerations when choosing between these data types:

• Storage space: nvarchar requires approximately double the storage
• Performance: varchar can be more performant for non-Unicode data due to less memory usage and processing overhead
• Future needs: Consider whether your application might eventually need Unicode support
• System constraints: Row size limitations and memory constraints may influence your choice
• Modern options: SQL Server 2019+ UTF-8 collations provide a middle ground with efficient Unicode storage

In practice, many applications benefit from a hybrid approach using varchar for known ASCII fields and nvarchar for fields that might contain international content or need future-proofing. Always test performance with your specific workload and data patterns to make the most informed decision for your particular use case.