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SQL Server Collation: A Complete Guide

SQL Server Collation: A Complete Guide

SQL Server collation plays a key role in how your database handles text. It defines how strings are sorted and compared—affecting everything from query behavior to data consistency. Whether you’re managing case sensitivity or supporting multiple languages, choosing the right collation ensures accurate and predictable results.

What is SQL Collation?

SQL collation is a set of rules that control how text data is sorted and compared in SQL Server. It determines if sorting is case-sensitive, whether accents matter, and how characters are ordered. When you create a database, table, or column, you set a collation to define these behaviors.

Collation settings influence several key aspects of character data handling:

Sort order: Controls the order in which characters are sorted. Some collations sort uppercase letters before lowercase.
Case sensitivity: Decides if “A” and “a” are treated as different. Case-sensitive collations treat them as separate characters.
Accent sensitivity: Determines if characters like “é” and “e” are treated the same or differently.

Why SQL Server Collation Matters

Choosing the right SQL Collation setting impacts performance, compatibility, and data accuracy:

Data integrity: Consistent collation ensures data is sorted and compared correctly across tables and databases. Mismatched collations can lead to unexpected query results and inconsistencies.
Query performance: Collations influence how efficiently SQL Server can optimize queries involving string data.
Cross-system compatibility: Aligning SQL Collation settings with those of other systems prevents corruption and comparison errors during integration.
Localization: Proper collation ensures accurate sorting and comparison for language-specific data. It’s critical to select one that fits your users’ locale.

How to Set SQL Collation in SQL Server

When creating a new SQL Server database, specify the default collation using the COLLATE clause:

CREATE DATABASE MyDatabase
COLLATE Latin1_General_CI_AS;

This example sets the collation to Latin1_General_CI_AS, which is case-insensitive and accent-sensitive.

You can also define collation at the column level:

CREATE TABLE Users (
Id INT PRIMARY KEY,
Name VARCHAR(50) COLLATE French_CI_AS

Here, the Name column uses French_CI_AS, optimized for French text comparison.

Understanding the SQL COLLATE Clause

The SQL COLLATE clause overrides default collation behavior for specific queries or fields. It gives developers flexibility when combining data from multiple sources or resolving mismatched collation errors.

For example, to join two tables with different collations, apply SQL Collation directly in the query:

SELECT *
FROM Users u
JOIN Customers c
ON u.Name COLLATE Latin1_General_CI_AS = c.Name COLLATE Latin1_General_CI_AS;

This SQL Collation example resolves mismatches and ensures accurate string comparison.

Choosing the Right SQL Collation

When selecting a collation, keep the following considerations in mind:

Language and locale: Choose a collation that supports the characters and sorting rules of your target language or region.
Case sensitivity: Decide whether uppercase and lowercase letters should be considered equal or distinct.
Accent sensitivity: Select a collation that suits your expectations for handling accented characters.
Compatibility: Ensure the chosen SQL Collation aligns with systems or services that interface with your database.
Performance: Some operations run faster with case-sensitive collations depending on how indexes are used.

Understanding SQL Collation Naming Convention

Collation names in SQL Server follow a pattern that reveals their behavior. For example, in Latin1_General_CI_AS:

Latin1_General: Specifies the locale or culture
CI: Case Insensitive
AS: Accent Sensitive

Other common abbreviations include:

CS: Case Sensitive
AI: Accent Insensitive
BIN: Binary sort order
BIN2: Improved binary sort order with better Unicode support

Understanding these suffixes helps you select a collation that fits your application’s sorting and comparison logic.

Common SQL Server Collations

SQL Server includes a wide array of collation options. Some of the most commonly used include:

SQL_Latin1_General_CP1_CI_AS: Default for US English. Case-insensitive, accent-sensitive.
Latin1_General_CS_AS: Case-sensitive and accent-sensitive. Suitable for more strict comparisons.
French_CI_AS: Best for French content; case-insensitive and accent-sensitive.
Japanese_CI_AS: For sorting and comparing Japanese characters.
Chinese_PRC_CI_AS: Designed for Simplified Chinese used in mainland China.

Refer to the official SQL Server documentation for a full list and compatibility considerations.

Collation Comparison Matrix

Here’s a quick comparison of common SQL Server collations and how they behave across case, accent, and binary sensitivity:

Collation	Case Sensitive	Accent Sensitive	Binary	Use Case
SQL_Latin1_General_CP1_CI_AS	No	Yes	No	Default for many US English installs
Latin1_General_CS_AS	Yes	Yes	No	Strict string comparisons
Latin1_General_BIN	Yes	Yes	Yes	Binary sort order, less readable
Latin1_General_BIN2	Yes	Yes	Yes	Better Unicode and deterministic sorting
Japanese_CI_AS	No	Yes	No	For full-width kana and locale support

Watch for Collation Mismatches in Joins

Joining tables from different databases—or even different columns in the same table—with mismatched collations will cause runtime errors like:

Cannot resolve collation conflict for equal to operation.

To avoid this:

Set a consistent collation at the database level when creating new environments
Use the COLLATE clause to resolve mismatches in legacy systems
Avoid ad-hoc overrides unless absolutely necessary—collation mismatches may silently change sort logic

Best Practices for Setting Collation

When starting a new SQL Server project, consider these tips:

Define collation at the server or database level from the beginning—retrofits are painful
Use _CI_AI collations for most modern applications unless strict case/accent matching is needed
Prefer BIN2 over BIN for better Unicode compliance and consistent index behavior
Document your chosen collation strategy—especially if teams are collaborating across systems

Changing SQL Collations

Sometimes, you may need to change collation after a database or table is created. SQL Server provides ALTER DATABASE and ALTER TABLE statements for this:

To modify the default collation of a database:

ALTER DATABASE MyDatabase
COLLATE French_CI_AS;

To update a column’s collation:

ALTER TABLE Users
ALTER COLUMN Name VARCHAR(50) COLLATE Latin1_General_CS_AS;

Here, the SQL Collation clause allows precise control without affecting the entire schema. It’s especially useful for resolving compatibility issues during integration or migration.

Changing collations can affect sorting and filtering logic, so be sure to validate results and test thoroughly before and after such changes.

Conclusion

SQL Collation plays a central role in how SQL Server handles sorting and comparison of character data. Understanding how to set, change, and override collation settings allows developers to avoid mismatches, optimize performance, and deliver language-aware applications.

Whether you’re managing a multilingual system or integrating data from external sources, SQL Collation gives you the precision and flexibility to maintain consistent query behavior across your infrastructure.