SQL Server Compatibility Level

What is SQL Server compatibility level and why is it important?

SQL Server compatibility level dictates the features and behaviors of your SQL Server database. It essentially controls the version of SQL Server your database behaves like. Choosing the correct level is crucial for maintaining compatibility and avoiding unexpected issues.

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Description

Example H2

Example H3

The SQL Server compatibility level is a crucial setting that determines the features and behaviors of your SQL Server database. It essentially acts as a time machine, allowing you to run your database as if it were a specific version of SQL Server. This is important because new features are often introduced in newer versions, and if you're using an older compatibility level, your database might not support those features. Conversely, using a newer compatibility level with an older database might cause issues with features that were only available in the older versions.For example, if your database is on compatibility level 150, it will behave like SQL Server 2019. If you try to use a feature introduced in SQL Server 2022, it might not work. Choosing the correct compatibility level ensures that your database behaves as expected and that you don't encounter any unexpected errors.Changing the compatibility level can have significant implications. It's not a simple task and should be done with careful consideration. If you change the compatibility level, you might need to adjust your stored procedures, functions, or other database objects to ensure they work correctly in the new environment. It's always a good idea to back up your database before making any changes.The compatibility level also affects how certain SQL statements are interpreted. For instance, syntax that was introduced in a newer version might not be recognized by an older compatibility level. Understanding the compatibility level of your database is essential for writing and maintaining efficient and reliable SQL code.In summary, the compatibility level is a critical aspect of SQL Server database management. It dictates the features and behaviors of your database, and choosing the correct level is essential for maintaining compatibility and avoiding unexpected issues. Careful planning and consideration are necessary when making changes to the compatibility level.

Why SQL Server Compatibility Level is important

Understanding compatibility levels is crucial for database administrators and developers to ensure that their databases function correctly and maintain compatibility with the intended SQL Server version. It prevents unexpected errors and ensures that applications and stored procedures work as expected. Choosing the right level is essential for long-term database stability and maintainability.

SQL Server Compatibility Level Example Usage


WITH RankedOrders AS (
    SELECT
        order_id,
        customer_id,
        order_date,
        ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY order_date) as order_rank
    FROM
        orders
)
SELECT
    order_id,
    customer_id,
    order_date,
    order_rank
FROM
    RankedOrders
WHERE
    order_rank BETWEEN 1 AND 3;

SQL Server Compatibility Level Syntax

Common Mistakes

Forgetting to back up the database before changing the compatibility level.
Not thoroughly testing the database after changing the compatibility level to identify potential issues.
Trying to use features from a newer version of SQL Server on an older compatibility level.
Failing to adjust stored procedures or other database objects after changing the compatibility level.

Frequently Asked Questions (FAQs)

Why is the SQL Server compatibility level often called a “time machine”?

Because it tells the engine to behave as if it were a specific historical version of SQL Server. Setting a database to compatibility level 150, for example, makes it follow the feature set and query-processing rules of SQL Server 2019 even if the underlying instance is newer. This lets legacy code continue to work while you plan an eventual upgrade.

What risks are involved in changing a database’s compatibility level, and how can I reduce them?

Raising or lowering the level can break stored procedures, functions, or queries that depend on version-specific syntax or optimizer behavior. To limit problems you should: (1) take a full backup, (2) test the change in a non-production environment, (3) re-compile and validate critical objects, and (4) review execution plans for regressions.

How can a modern SQL editor like Galaxy help when working across different compatibility levels?

Galaxy’s AI copilot understands your schema and SQL Server version, so it can autocomplete only the functions available at a given compatibility level and flag unsupported syntax before it reaches production. You can also collaborate with teammates by sharing version-specific queries in Collections, ensuring everyone runs code that matches the database’s current level.