On one occasion I overheard SQL pronounced as squeal.

Stunned into silence.

Many people use 'seaqual' if that is what you mean.. I don't think it is rare.

"Squeal", like a pig. Not "Sequel" like 'Babe: pig in the city'.

The nice thing about SQL and URL is that they're so widely used in our profession that regardless of how you say them you will be understood easily. Some people say "ess que ell" and others say "sequel" and that's fine; everyone understands everyone.

It's unconventional pronunciations of less common initialisms that cause problems.

May I lament at this point that we non native speakers often miss out on the pun entirely and read brand-/projectnames as abstract fantasy words.

SQL -> "sequel", how could we know?

"Sequel", or "skewl" when I'm in a hurry. Who has time to say "ess que ell"?

A friend of mine, who is not a fan of database work, pronounces it "squeal".

That's why I say "postgres", not "postgre sql".

What about Postgres Cue Ell?

squirrel :)