MSSQL to MySQL Converter — Preserve Schema & Stored ProceduresMigrating a database from Microsoft SQL Server (MSSQL) to MySQL can be a complex task, especially when you need to preserve not just tables and data but also the schema details and business logic implemented with stored procedures, functions, triggers, views, and constraints. A reliable MSSQL to MySQL converter simplifies this process by translating data types, DDL/DML syntax, and procedural code while minimizing manual fixes. This article explains the challenges you’ll face during migration, the steps a good converter should take, practical strategies for preserving schema and stored procedures, and tips for testing and post-migration optimization.
Why Migrate from MSSQL to MySQL?
Organizations choose to migrate from MSSQL to MySQL for several reasons:
- Cost savings: MySQL is open-source (with commercial options), often reducing licensing costs.
- Platform independence: MySQL runs on many operating systems and cloud platforms.
- Ecosystem: MySQL integrates well with PHP-based applications and many modern web stacks.
- Performance and scaling choices: Depending on workload, MySQL variants (InnoDB, MyRocks) and cloud offerings can be more suitable.
While benefits are compelling, migrations require caution—especially where stored procedures and complex schema features are involved.
Key Differences Between MSSQL and MySQL
A converter must handle differences at multiple levels:
- Data types: MSSQL has types like UNIQUEIDENTIFIER, DATETIME2, MONEY; MySQL uses UUIDs as strings or native UUID functions, DATETIME, DECIMAL.
- Identity/auto-increment: MSSQL uses IDENTITY(n, s); MySQL uses AUTO_INCREMENT.
- Schema structure: MSSQL supports schemas (dbo, app); MySQL historically uses databases as namespaces, though recent versions support schemas via catalogs.
- Procedural languages: MSSQL’s T-SQL differs from MySQL’s stored routine syntax (BEGIN…END, different variable declarations, error handling).
- Functions and built-ins: Date functions, string functions, and system functions often differ.
- Transaction and locking behavior: Default isolation levels and locking nuances vary.
- Views and indexed views: MySQL doesn’t directly support indexed views the same way MSSQL does.
- Triggers: Different timing, multiple triggers per event support, and pseudo-tables (INSERTED/DELETED) handling.
What a Good Converter Should Do
A capable MSSQL to MySQL converter should:
- Analyze and map schema objects: tables, columns, constraints, indexes, sequences, and identity columns.
- Translate data types sensibly, preserving precision and scale.
- Convert T-SQL stored procedures, functions, and triggers into MySQL-compatible routines, handling:
- Variable declarations and scope
- Flow control (IF, WHILE, CASE)
- Error handling (TRY…CATCH –> handlers)
- Cursor usage
- Temporary tables and table variables
- Rewrite queries and DML where syntax differs (TOP vs LIMIT, APPLY, MERGE).
- Handle dependencies and object creation order.
- Generate migration scripts and optionally perform data transfer.
- Provide reports of items that need manual review (e.g., CLR procedures, unsupported T-SQL features).
Step-by-Step Migration Workflow
- Assessment and inventory
- Catalog all database objects and dependencies.
- Identify unsupported features (CLR, SQL Server Agent jobs) and external integrations.
- Schema conversion
- Use the converter to generate CREATE statements for MySQL.
- Review data type mappings and adjust where precision/scale matters (e.g., MONEY → DECIMAL(19,4)).
- Stored procedure and function conversion
- Translate procedural code; convert TRY/CATCH to DECLARE HANDLER; change variable declarations.
- Replace proprietary functions with MySQL equivalents or implement user-defined functions.
- Data migration
- Export/import data via bulk tools, scripts, or the converter’s transfer utilities.
- Preserve encoding (UTF-8) and handle large objects (BLOB/CLOB) carefully.
- Testing and validation
- Run schema comparisons and row counts.
- Validate stored procedure outputs with unit/integration tests.
- Test performance and query plans; add indexes if needed.
- Cutover and monitoring
- Plan downtime or run in parallel during test period.
- Monitor for data drift and performance regressions.
Translating Stored Procedures: Common Patterns
- Variable declarations
- MSSQL: DECLARE @cnt INT = 0;
- MySQL: DECLARE cnt INT DEFAULT 0;
- Error handling
- MSSQL: TRY…CATCH
- MySQL: DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN … END;
- Top vs Limit
- MSSQL: SELECT TOP 10 * FROM table;
- MySQL: SELECT * FROM table LIMIT 10;
- String concatenation
- MSSQL: ‘a’ + ‘b’
- MySQL: CONCAT(‘a’,‘b’)
- IF EXISTS (drop)
- MSSQL: IF OBJECT_ID(‘dbo.t’,‘U’) IS NOT NULL DROP TABLE dbo.t;
- MySQL: DROP TABLE IF EXISTS t;
- Temporary tables
- MSSQL: CREATE TABLE #temp(…)
- MySQL: CREATE TEMPORARY TABLE temp(…)
Handling Unsupported or Complex Features
- CLR Stored Procedures and Extended Features: Rewrite in application code or as MySQL UDFs if necessary.
- SQL Server Agent Jobs: Move scheduling to cron, systemd timers, or a job scheduler (e.g., Airflow).
- Service Broker, XML indexes, Spatial types: Evaluate on a case-by-case basis; use alternative MySQL features or external services.
- MERGE statements: Convert to INSERT … ON DUPLICATE KEY UPDATE or use separate INSERT/UPDATE logic.
Testing Checklist
- Row counts per table match after migration.
- Referential integrity preserved and foreign keys enforced.
- Stored procedures produce identical outputs for representative inputs.
- Performance testing on critical queries and transactions.
- Backup and restore procedures work on the target MySQL server.
Performance and Optimization Tips Post-Migration
- Review indexes—MySQL optimizer may prefer different keys.
- Use EXPLAIN to inspect query plans; consider rewriting costly queries.
- Ensure InnoDB configuration (buffer pool size, log file size) matches workload.
- Enable slow query log and tune based on real usage.
- Consider partitioning large tables if needed.
Tools and Resources
There are several tools that can assist with MSSQL to MySQL migration:
- Native tools: MySQL Workbench migration wizard supports MSSQL as a source.
- Commercial/third-party converters: offer advanced procedural translations and automated data transfer.
- Scripting and ETL tools: Pentaho, Talend, custom Python scripts using pyodbc and mysql-connector.
Common Pitfalls
- Blindly trusting automated conversions for stored procedures—manual review is almost always required.
- Ignoring collation and character set differences—can cause subtle bugs with string comparison and sorting.
- Underestimating downtime or the complexity of cutover for systems with heavy write loads.
Conclusion
Migrating from MSSQL to MySQL while preserving schema and stored procedures is feasible but requires careful planning, the right converter, and thorough testing. Focus on accurate type mapping, careful translation of T-SQL constructs, and validating procedural behavior. With the right approach, you can minimize manual rework and retain critical business logic during migration.