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There's probably a couple reasons, but I'll summarize my experiences with them. I haven't dug into MySQL for a few years (last I really worked with it was 5.5), but out of the box, it does a lot of things that are pretty unsafe or encourage bad practices, such as truncating data when it's longer than the column size, inserting the zero-value for a NOT NULL column rather than erroring when a NULL is inserted, confusing timestamp column behavior, no DDL-level transactionality, etc. Additionally, and not necessarily a bad thing, but it has made some odd implementation and feature decisions that can be (IMHO) counter-intuitive or have a large impact, particularly with regards to how foreign keys get implemented, but also with things like not having schemas (database > tables, rather than database > schemas > tables), not having a boolean type, its datatype specification (int(1) means an integer that displays only a single digit, rather than denoting storage sizes), or the fact that every ALTER TABLE causes a complete on-disk table rewrite. PostgreSQL, on the other hand, makes every attempt to keep 100% data integrity at all times, has a lot of killer features (probably the best date/time math implementation I've ever used, typesafe operators, etc), is generally very extensible, and most importantly, is extremely predictable. True, it doesn't have the same scalability features out of the box that MySQL does, but that's getting better every release, and as mentioned elsewhere, there's plenty of adequate third-party tooling available (e.g. Slony). I think MySQL is very much so the PHP of the RDBMS world - it does a lot of silly stupid stuff - mostly for historical reasons - but in the hands of someone who knows how to use it properly, it can be an extremely useful tool. Postgres just defaults to being an extremely useful tool out of the box without needing to know all the gotchas that come with it. |
This is no longer the default in MySQL 5.7.