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Migrating from Microsoft SQL Server (MSSQL) to MySQL can help organizations reduce database licensing costs, adopt more flexible infrastructure, and align their databases with application requirements. However, a successful migration involves more than transferring tables and records. Differences in data types, SQL syntax, database objects, and transaction behavior must be addressed to ensure the target database works correctly.
This guide explains how to migrate MSSQL to MySQL step by step, from initial assessment and schema conversion to data synchronization, validation, and production cutover. It also compares common migration tools and outlines practical steps for minimizing migration risks.
Organizations may consider migrating from SQL Server to MySQL for several reasons, depending on their application architecture and infrastructure strategy.
Reduce database licensing costs: MySQL Community Edition is open-source software, which may help reduce licensing expenses. Total costs still depend on infrastructure, support, and operational requirements.
Support flexible deployment: MySQL can run across different operating systems and infrastructure environments, including cloud platforms.
Align with application requirements: Applications built around open-source technologies may benefit from using MySQL as their database platform.
Simplify infrastructure planning: Moving to MySQL may support platform standardization and cloud adoption when the target environment meets workload requirements.
Before migrating, evaluate whether MySQL supports your application’s database features, performance requirements, and operational needs. The expected benefits should justify the work required to convert database objects and adapt applications.
Although SQL Server and MySQL are both relational database management systems, they differ in data types, SQL syntax, database structures, and runtime behavior. Identifying these differences early helps prevent errors during migration.
Some SQL Server data types do not have direct MySQL equivalents. Examples include UNIQUEIDENTIFIER, MONEY, SMALLDATETIME, and certain legacy large-text types.
The following table illustrates common mapping considerations:
| SQL Server | Common MySQL option | What to check |
|---|---|---|
IDENTITY |
AUTO_INCREMENT |
Existing identifiers and sequence behavior |
UNIQUEIDENTIFIER |
CHAR(36) or BINARY(16) |
Storage format and application compatibility |
MONEY |
DECIMAL(p,s) |
Required precision and scale |
DATETIME2 |
DATETIME(fsp) |
Fractional-second precision |
NVARCHAR(n) |
VARCHAR(n) with an appropriate character set |
Character encoding and length semantics |
These are starting points rather than universal one-to-one replacements. Choose target types based on the source data, application requirements, and supported MySQL version. Pay particular attention to financial values, identifiers, timestamps, and character encoding to avoid data loss or unexpected behavior.
SQL Server uses Transact-SQL (T-SQL), while MySQL has its own SQL syntax and supported database features. Queries, stored procedures, triggers, functions, and other database objects may require modification.
For example, SQL Server commonly uses TOP to limit query results, whereas MySQL uses LIMIT.
SQL Server:
SELECT TOP (10) *
FROM Customers
ORDER BY CustomerID;MySQL:
SELECT *
FROM Customers
ORDER BY CustomerID
LIMIT 10;Other differences may involve date functions, conditional expressions, identity columns, error handling, and transaction behavior.
Do not assume that transferring table data automatically makes the application compatible with MySQL. Review application queries and database objects separately, and test converted logic before production cutover.
SQL Server supports multiple schemas within a database, whereas MySQL organizes database objects differently. Schema names, object ownership, permissions, and naming conventions may need adjustment.
Map the source database structure to the target design before transferring production data. Identify dependencies between tables, views, procedures, triggers, and other objects so that they can be converted and deployed in the correct order.
Applications may rely on SQL Server-specific queries, drivers, connection settings, or database behaviors. These dependencies can cause errors even when the underlying data has been migrated successfully.
MySQL may also require different indexes, query plans, or configuration settings to achieve the desired performance. Test representative application workloads and review slow queries before switching production traffic.
A large database can take considerable time to transfer. Meanwhile, the source database may continue receiving inserts, updates, and deletes.
Without a mechanism to capture and apply ongoing changes, the target may become outdated before cutover. A suitable migration plan should define how to synchronize changes, validate consistency, coordinate the application switch, and recover if the transition fails.
Preparation helps identify compatibility problems before they affect production systems.
Complete the following checks before starting:
Inventory the source database: Record database size, tables, indexes, views, stored procedures, triggers, dependencies, and scheduled jobs.
Review compatibility: Identify unsupported data types, T-SQL dependencies, and database objects that require conversion.
Design the target schema: Define MySQL data types, character sets, collation, indexes, constraints, and naming conventions.
Estimate migration time: Consider data volume, network bandwidth, source write activity, and the available cutover window.
Define validation criteria: Establish how to verify row counts, critical field values, application behavior, and data consistency.
Prepare a rollback plan: Define the conditions for stopping the cutover and the steps required to restore service if validation fails.
Also, verify source and target version compatibility, review the migration tool’s supported objects and data types, and test schema conversion and incremental synchronization in a staging environment. Resolve compatibility issues before migrating production data.
The following workflow covers the main stages of a SQL Server to MySQL migration. The exact process depends on database size, application dependencies, the selected tools, and acceptable downtime.
Begin by examining the SQL Server environment and identifying the objects and data that must be migrated.
Review table structures, primary and foreign keys, indexes, stored procedures, triggers, views, scheduled tasks, and application dependencies. Identify SQL Server-specific features and determine how each will be handled in MySQL.
Next, define the migration scope. Decide whether the project involves a complete database, selected tables, or a phased transition. Establish the expected data volume, acceptable downtime, and performance requirements before selecting a migration method.
Create a compatible schema in MySQL before transferring the production data.
Map SQL Server data types to appropriate MySQL types, then review default values, constraints, indexes, identity columns, and character encoding. Convert SQL Server-specific queries and database objects where necessary.
For example, a SQL Server IDENTITY column may be implemented using MySQL’s AUTO_INCREMENT, depending on the target design. Check existing identifier values and application dependencies before applying the conversion.
Validate the converted schema before proceeding. Confirm that tables, indexes, and constraints have been created correctly, and test converted database objects against representative queries.
Once the target schema is ready, transfer the existing records from SQL Server to MySQL.
The appropriate method depends on database size, network conditions, migration frequency, and operational requirements. A small database may be migrated using export and import utilities, while a larger production database may benefit from a dedicated migration tool.
During the initial transfer:
Monitor migration progress and identify failed records.
Investigate conversion errors and interrupted operations.
Compare source and target row counts for critical tables.
Validate representative records and important field values.
If the source database remains active during the transfer, plan how changes made after the initial data copy begins will be captured and applied to MySQL.
For production systems that cannot remain offline throughout the migration, ongoing change synchronization can help reduce the final cutover window.
After the initial data transfer, a compatible replication solution can capture supported changes from SQL Server and apply them to MySQL. Depending on the tool and configuration, this can include inserts, updates, and deletes.
Information2 Software’s i2Stream is designed for heterogeneous database replication and real-time data synchronization. It can be evaluated for MSSQL-to-MySQL migration scenarios where the target database needs to stay updated while the source continues handling business transactions.
During synchronization, monitor replication status, errors, and lag between the source and target. Before cutover, verify that all required changes have been applied and that the target meets the project’s consistency criteria.
Real-time synchronization reduces the amount of data left to process during cutover, but it does not eliminate the need for application testing, final validation, or rollback planning.
Before directing production traffic to MySQL, confirm that the target database is ready for use.
Use this cutover checklist to coordinate the final transition:
Confirm readiness: Verify that schema conversion, application testing, and initial data validation are complete.
Control source writes: Pause application writes or place the source in an appropriate maintenance state according to the migration plan.
Finish synchronization: Allow pending changes to be applied and confirm that replication has caught up.
Validate the target: Recheck critical row counts, key values, constraints, and application queries.
Switch application connections: Update the required connection settings and direct application traffic to MySQL.
Monitor production: Check application logs, error rates, transaction behavior, and query performance.
Apply rollback criteria: If critical validation checks fail, follow the documented recovery plan rather than continuing with an unstable target.
Keep the source environment available according to the rollback plan. Before directing production traffic back to SQL Server, account for any writes made to MySQL after cutover to avoid losing or overwriting data.
The right migration tool depends on database size, object compatibility, infrastructure, and whether ongoing synchronization is required.
MySQL Workbench provides a Migration Wizard for supported source databases and migration scenarios. It can assist with schema conversion and data transfer.
It may suit projects that fit its supported capabilities. However, complex stored procedures, application dependencies, and ongoing production synchronization may require additional tools or manual work.
AWS DMS supports database migration and ongoing replication for supported source and target configurations. It can be useful for migrations involving AWS infrastructure or workflows that require an initial load followed by change data capture.
Review the supported engine versions, migration limitations, and service requirements. Schema conversion and database-object compatibility may require separate assessment or conversion work.
i2Stream focuses on heterogeneous database replication and real-time data synchronization. It is worth evaluating when an MSSQL-to-MySQL migration requires ongoing synchronization between the source and target before production cutover.
Its replication management and task monitoring can help teams track synchronization progress and identify errors. As with any migration solution, the implementation should be based on the supported database configurations and the project’s specific requirements.
Choose the tool that best fits your migration scope, consistency requirements, downtime limits, and operational capabilities rather than selecting one solely by the number of features it offers.
Apply these practices throughout the migration to improve reliability and reduce production risk.
Run a pilot migration: Test representative tables and database objects before migrating the full dataset.
Validate data beyond row counts: Compare important field values, constraints, and application behavior.
Monitor synchronization continuously: Investigate replication errors and lag before scheduling cutover.
Test real application workloads: Check query performance, transaction behavior, and application compatibility on MySQL.
Document conversion decisions: Record schema changes, unsupported objects, exceptions, and validation results.
These checks help teams identify issues early and make the production transition more predictable.
Can I migrate MSSQL to MySQL without downtime?
A migration can be designed to minimize downtime by combining an initial data transfer with ongoing change synchronization. The final cutover may still require a brief write pause or application interruption, depending on the architecture and consistency requirements.
What is the difference between MSSQL and MySQL migration?
MSSQL-to-MySQL migration involves moving data between two database systems with different SQL dialects, data types, and object models. Schema conversion, database code compatibility, and application testing are therefore important in addition to data transfer.
Which tool is best for MSSQL to MySQL migration?
The right tool depends on the migration scope. MySQL Workbench may suit supported schema conversion and data transfer scenarios, AWS DMS may fit supported migration and replication workflows, and i2Stream may be suitable when heterogeneous database replication and real-time synchronization are required.
Do I need to rewrite stored procedures when migrating from SQL Server to MySQL?
Some stored procedures, functions, triggers, and queries may need to be rewritten because SQL Server uses T-SQL and MySQL has different syntax and database features. Review each object and test the converted implementation before production cutover.
How do I verify data after migrating MSSQL to MySQL?
Compare row counts, key values, constraints, and representative records. Test application queries, transaction behavior, and performance as well. If ongoing synchronization is used, confirm that all required source changes have been applied before switching production traffic.
Migrating MSSQL to MySQL requires careful planning, schema conversion, reliable data transfer, and thorough validation. For production systems, combining an initial migration with ongoing synchronization can help reduce the final cutover window while the source database remains active.
By assessing compatibility early, testing the migration process, and preparing a clear cutover and rollback plan, organizations can make the transition more predictable. When real-time synchronization between heterogeneous databases is required, i2Stream is an option to evaluate for the migration workflow.
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