Challenges of Porting Mixed Identifiers Between Oracle and PostgreSQL

When migrating a database from Oracle to PostgreSQL, one of the most common challenges that developers face is dealing with the differences in how the two databases handle mixed identifiers. In Oracle, identifiers are case-insensitive by default, whereas PostgreSQL treats them as case-sensitive. This can lead to issues when porting code and SQL queries from Oracle to PostgreSQL, especially when dealing with mixed-case identifiers.

In this blog post, we will explore the challenges of porting mixed identifiers between Oracle and PostgreSQL, and discuss best practices for handling these differences.

Understanding the Differences

In Oracle, identifiers are not case-sensitive by default. This means that the following statements are considered the same in Oracle:

SELECT * FROM employees;
SELECT * FROM EMPLOYEES;
SELECT * FROM Employees;

On the other hand, PostgreSQL treats identifiers as case-sensitive by default. This means that the above statements would be considered different in PostgreSQL.

When porting code and SQL queries from Oracle to PostgreSQL, it is important to take these differences into account to ensure that the ported queries and code behave as expected in the new environment.

Best Practices for Porting Mixed Identifiers

1. Use Quoted Identifiers

One way to handle mixed identifiers when porting from Oracle to PostgreSQL is to use quoted identifiers. In PostgreSQL, quoted identifiers are always case-sensitive, regardless of the standard_conforming_strings setting.

For example, in PostgreSQL, the following statement defines a table with a mixed-case column name:

CREATE TABLE employees (
    "employeeID" INTEGER,
    "employeeName" VARCHAR(100)
);

By using quoted identifiers, you can ensure that the identifiers are treated as case-sensitive in both Oracle and PostgreSQL, making the transition between the two databases smoother.

2. Update Code and Queries

Another best practice when porting mixed identifiers is to update the code and queries to use consistent casing for identifiers. This not only simplifies the porting process but also improves the readability and maintainability of the code.

For example, instead of writing queries with mixed-case identifiers like this:

SELECT "employeeID", "employeeName" FROM employees;

You can update the identifiers to use a consistent casing, such as:

SELECT "employee_id", "employee_name" FROM employees;

By using consistent casing for identifiers, you can avoid potential issues when porting between Oracle and PostgreSQL, and make the code more standardized and easier to understand.

3. Adjust Configuration Settings

In some cases, you may need to adjust the configuration settings in PostgreSQL to handle mixed identifiers more effectively. For example, you can set the standard_conforming_strings parameter to off in PostgreSQL to make string handling more similar to Oracle.

Additionally, you can set the quote_all_identifiers parameter to on to force PostgreSQL to always treat unquoted identifiers as case-sensitive. These configuration tweaks can help make the transition from Oracle to PostgreSQL smoother when dealing with mixed identifiers.

Closing Remarks

Porting mixed identifiers between Oracle and PostgreSQL can be a challenging task, but by understanding the differences in how the two databases handle identifiers and following best practices, you can ensure a smoother transition. Using quoted identifiers, updating code and queries for consistent casing, and adjusting configuration settings in PostgreSQL are all effective strategies for handling mixed identifiers during the migration process.

By following these best practices, you can minimize the impact of the differences between Oracle and PostgreSQL when dealing with mixed identifiers, and ensure that your code and SQL queries work seamlessly in the new database environment.