German Collation Comparison as NVARCHAR

Overview

In this article, we will explore the nuances of collation comparisons in SQL Server. Specifically, we will examine why converting strings to NVARCHAR can affect collation comparisons and provide a solution to this issue.

Introduction to Collations

Collations are a crucial aspect of database design, as they determine how string data is compared and sorted. SQL Server supports various collations, each with its own set of rules for comparing characters.

The Collation Comparison Problem

The question at the heart of this article revolves around German special character ‘ß’ (eszett) in collation comparisons. The issue arises when using NVARCHAR to store and compare strings containing this character.

Consider the following example:

SELECT name, collation_name
FROM sys.databases
WHERE name = N'DBName';

In this query, we cast two strings, ‘Steds.Weßels’ (German special character) and ‘Steds.Wessels’, to NVARCHAR(100). When using the = operator for comparison, SQL Server treats these characters as equal. However, when comparing them using a hardcoded string literal, the result is different.

Why Does Conversion Impact Collation Comparison?

The reason behind this discrepancy lies in how SQL Server handles collations and character comparisons.

When using a specific collation (in this case, SQL_Latin1_General_CP1_CI_AS), SQL Server follows these rules for comparing characters:

‘ä’ is equivalent to ‘a’
‘ö’ is equivalent to ‘o’
‘ü’ is equivalent to ‘u’

These equivalencies are defined by the collation’s character set and code page.

When converting strings to NVARCHAR, which typically uses UTF-8 encoding, SQL Server can no longer rely on these specific equivalencies. In UTF-8, the German special character ‘ß’ has a unique Unicode code point (U+00SS).

Therefore, when comparing characters using NVARCHAR, SQL Server treats ‘ß’ and ‘ss’ as distinct characters.

Changing to VARCHAR: A Solution

The solution to this issue involves changing the data type of columns that store strings containing German special characters from NVARCHAR to VARCHAR. This allows SQL Server to follow its specific collation rules for comparing characters.

To demonstrate this, consider the following example:

IF 'Steds.Weßels' = 'Steds.Wessels'
BEGIN
    SELECT 'Equal';
END
ELSE
BEGIN
    SELECT 'Not equal';
END;

In this query, we compare two strings using a hardcoded string literal. Because SQL Server is using the SQL_Latin1_General_CP1_CI_AS collation, it correctly treats ‘ß’ and ‘ss’ as distinct characters.

In contrast, if we were to convert these strings to NVARCHAR:

IF CAST('Steds.Weßels' AS VARCHAR(100)) = CAST('Steds.Wessels' AS VARCHAR(100))
BEGIN
    SELECT 'Equal';
END
ELSE
BEGIN
    SELECT 'Not equal';
END;

In this case, the comparison would return False (or “Not equal”), because SQL Server treats ‘ß’ and ‘ss’ as distinct characters in NVARCHAR.

Conclusion

Collation comparisons can be tricky, especially when dealing with special characters like German ‘ß’. Understanding how collations work and why conversion impacts these comparisons is crucial for ensuring accurate data analysis and manipulation.

By changing the data type of columns from NVARCHAR to VARCHAR, you can ensure that SQL Server follows its specific collation rules for comparing characters. This may require adjustments to your database design and query writing practices, but it will ultimately help you achieve more reliable and accurate results.

Last modified on 2024-11-10