Oracle XE will have the deepest SQL/PSM implementation of any freely-available database, without question. The list of standard functions, procedures and packag

Oracle XE will have the deepest SQL/PSM implementation of any freely-available database, without question. The list of standard functions, procedures and packages is enormous. This is a double-edged sword. If you use these (proprietary) features and you outgrow XE, then you have to buy a license. XE also doesn't get quarterly patches - it's updated every couple of years (hardening is essential). Oracle Enterprise retails for $47,500/CPU core. The stripped-down SE2 falls to about $18k. Definitely beware of the lock-in, but XE likely remains the best for procedural programming in SQL. For the extremely Oracle-averse, there still may be some value in running it alongside Postgres(with the SQL/PSM extension) and MySQL to verify that your code is portable.