Database30 September 2025·10 min read

MySQL to PostgreSQL Migration: A Step-by-Step Guide

Why teams migrate from MySQL to PostgreSQL, data type mapping, migration tools like pgLoader and AWS DMS, testing strategies, and post-migration validation.

MySQLPostgreSQLMigrationDatabasepgLoaderAWS DMS

Why Teams Migrate from MySQL to PostgreSQL

MySQL has served the web well for decades. It powers WordPress, countless Laravel applications, and was the "M" in the LAMP stack. But teams increasingly migrate to PostgreSQL for several compelling reasons:

Advanced data types: PostgreSQL natively supports JSONB, arrays, ranges, UUIDs, and custom types. MySQL has JSON support but it is less mature.

Full ACID compliance: PostgreSQL's MVCC implementation provides true serializable isolation. MySQL's InnoDB is ACID compliant but its default isolation level (REPEATABLE READ) has subtle differences.

Extensions: PostGIS for geographic data, pg_trgm for fuzzy text search, pgvector for AI embeddings — PostgreSQL's extension ecosystem is unmatched.

Standards compliance: PostgreSQL follows the SQL standard more closely, making queries more portable.

Window functions and CTEs: PostgreSQL's support for advanced SQL features like recursive CTEs, lateral joins, and window functions is more complete.

Pre-Migration Assessment

Before migrating, assess the scope:

Data Type Mapping

MySQL TINYINT(1) maps to PostgreSQL BOOLEAN

MySQL DATETIME maps to PostgreSQL TIMESTAMP WITHOUT TIME ZONE

MySQL AUTO_INCREMENT maps to PostgreSQL SERIAL or GENERATED ALWAYS AS IDENTITY

MySQL ENUM maps to PostgreSQL custom types (CREATE TYPE) or CHECK constraints

MySQL DOUBLE maps to PostgreSQL DOUBLE PRECISION

MySQL TEXT/MEDIUMTEXT/LONGTEXT all map to PostgreSQL TEXT (no size variants needed)

MySQL UNSIGNED integers have no PostgreSQL equivalent — use CHECK constraints or larger integer types

SQL Syntax Differences

Identifier quoting: MySQL uses backticks (`table`), PostgreSQL uses double quotes ("table")

String concatenation: MySQL uses CONCAT(), PostgreSQL supports both CONCAT() and the || operator

LIMIT syntax: Both support LIMIT/OFFSET, but MySQL's LIMIT offset, count syntax is not supported in PostgreSQL

Boolean handling: MySQL uses 0/1, PostgreSQL uses TRUE/FALSE

Case sensitivity: PostgreSQL identifiers are case-sensitive when quoted, MySQL depends on the OS and configuration

Migration Tools

pgLoader

pgLoader is an open-source tool specifically designed for migrating to PostgreSQL. It reads from MySQL directly and writes to PostgreSQL, handling data type conversions automatically. It supports continuous migration with Change Data Capture for minimal downtime.

Install pgLoader, create a migration command file specifying the MySQL source and PostgreSQL target connection strings, configure type casting rules, and run. pgLoader handles schema creation, data transfer, index creation, and foreign key constraints.

AWS Database Migration Service (DMS)

For AWS-hosted databases, DMS provides managed migration with ongoing replication. Create a replication instance, configure source and target endpoints, create a migration task, and DMS handles the rest. It supports full load plus change data capture for near-zero downtime migrations.

Manual Migration with pg_dump Format

For smaller databases, export from MySQL using mysqldump, transform the SQL using sed or a conversion script, and import into PostgreSQL. This approach gives you maximum control but requires more manual effort.

Testing Strategies

Data Validation

Compare row counts for every table between source and target

Hash-compare random samples of rows to verify data integrity

Validate that auto-increment sequences are correctly set in PostgreSQL

Test NULL handling — MySQL and PostgreSQL treat NULLs slightly differently in some edge cases

Application Testing

Run your full test suite against the PostgreSQL database

Test all ORM queries — some may use MySQL-specific syntax

Load test with production-like traffic to identify performance differences

Test edge cases: Unicode handling, timezone conversions, large text fields

Common Pitfalls

Group by strictness: PostgreSQL requires all non-aggregated columns in the SELECT to appear in GROUP BY. MySQL's ONLY_FULL_GROUP_BY mode is similar but was optional until recently.

Case sensitivity in LIKE: PostgreSQL LIKE is case-sensitive. Use ILIKE for case-insensitive matching.

Zero dates: MySQL allows 0000-00-00 as a date. PostgreSQL does not. Convert these to NULL or a sentinel date before migration.

Implicit type casting: MySQL is more permissive with implicit casts. PostgreSQL requires explicit casting in many cases.

Post-Migration Validation

Monitor query performance for the first week — some queries may need new indexes optimized for PostgreSQL's query planner

Verify that VACUUM and ANALYZE are running properly (PostgreSQL's autovacuum handles this by default)

Check that connection pooling is configured (PgBouncer or built-in pooling in your hosting provider)

Update your backup and monitoring tools for PostgreSQL

Migration is a significant effort, but teams consistently report that PostgreSQL's capabilities justify the investment. Need help planning your migration? Get in touch.

The Beyond Horizon Team

Engineering-led digital studio based in India. We build production-grade web apps, mobile apps, AI systems, and SaaS platforms — and write about what we learn along the way.

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