Stored procedures and functions are crucial components of a database system that encapsulate data processing logic. Although SQL Server and PostgreSQL share similar syntax rules for composing these objects, there are differences between them. One key distinction is that SQL Server’s T-SQL allows for dynamic determination of result sets returned by a procedure, whereas PostgreSQL does not. As a result, migrating stored procedures and functions from SQL Server or Azure SQL to PostgreSQL can be a complex task that requires expertise and careful consideration.
When migrating the source code of stored procedures, functions and triggers from MS SQL or Azure SQL to PostgreSQL, all embedded functions and operators must be rewritten according to the target dialect of SQL. Therefore, it is important to research best practices for translating basic syntax constructions, ensuring that the underlying problem is fully understood, rather than just formal conversion of tokens and its combinations. Pay special attention to the fact that local variables in PostgreSQL functions must be declared at the beginning, while SQL Server allows variables to be declared anywhere, which requires a change in habit.
One of the most significant differences between SQL syntax of MS SQL and PostgreSQL are exposed in triggers. In SQL Server or Azure SQL, the trigger’s code goes as a part of CREATE TRIGGER statement. On the other hand, PostgreSQL requires the code of trigger is composed as standalone function and reference to that function from CREATE TRIGGER statement.
To simplify the migration process, special automation tools like the SQL Server to PostgreSQL Code Converter may be used. This product is offered by Intelligent Converters software company. It can partially automate the migration of database logic entries from SQL Server or Azure SQL to PostgreSQL. This product can migrate stored procedures, functions, triggers, and views, convert MS SQL built-in functions into PostgreSQL equivalents, map predefined MS SQL types into PostgreSQL, and handle reserved words and identifiers intelligently. For those cases when direct connection to SQL Server or Azure SQL is not available, the source code may be extracted not only from the database but also from T-SQL script file.
Although the SQL Server to PostgreSQL Code Converter can automate the migration of basic syntax patterns and constructions, some manual post-processing of the output code may be necessary, particularly for large and complex fragments of the source code.
In conclusion, a successful migration of stored procedures and functions from SQL Server or Azure SQL to PostgreSQL requires a deep understanding of both database systems and careful consideration of their differences in syntax and functionality. Following best practices for translating stored procedures and functions, database engineers and other responsible staff can ensure a smooth migration. While tools like the SQL Server to PostgreSQL Code Converter can simplify the process, manual post-processing may still be necessary for complex source code fragments.
