Sampling with SQL

Is there something in the SQL standard that says functions are guaranteed to executed more than once?

I swear that once I used something like random() and it was only executed once, making it useless for the task at hand. I had to use some trick to ensure it was executed for each row.

I may have used it in the `select` part. Dialect was Oracle's, from memory.

related: https://xkcd.com/221/

It depends on the function and the SQL implementation, you can see in this simulator that where rand() > rand() evaluates row by row in MySQL but once in SQL Server, so its easy to get this stuff messed up even if the code is "equivalent" its really not.

https://onecompiler.com/mysql/42vq8s23b https://onecompiler.com/sqlserver/42vq8tz24

Thanks, that's a bit upsetting :-)