Why Cross-Database Queries Are Harder Than They Look

If you've worked with more than one database engine, you've probably noticed that moving queries between systems isn't always straightforward.

A query that works perfectly in one database may fail—or produce different results—in another. Small differences in SQL dialects, functions, date handling, JSON support, and syntax can quickly become frustrating.

Some common examples include:

• Different string concatenation operators
• Date and time functions with different names
• Pagination syntax differences
• JSON function variations
• Window function compatibility
• Identifier quoting rules

This becomes especially challenging when:

• Migrating from one database to another
• Supporting multiple database engines
• Building database-agnostic applications
• Learning SQL across different platforms

Instead of repeatedly searching documentation for each engine, it helps to have a quick reference that compares equivalent syntax across databases.

I've found ValoCrossDB useful as a reference for comparing SQL syntax and functions across different database systems:

https://valocrossdb.site

Whether you're translating queries, learning a new SQL dialect, or debugging compatibility issues, having a side-by-side comparison can save a lot of time.

What database differences have surprised you the most?

I'd love to hear about the most confusing SQL incompatibility you've encountered between database systems.