Should you ever use MySQL when Postgres is a superior DBMS?

• MySQL is easy to set up

  So is PostgreSQL; I find it way easier to set up than MySQL. Neither involve "rocket surgery," and PostgreSQL has an advantage for cases where you want to use transactional capabilities, in that there's no need to install or configure any extra add-ons that mayn't come from MySQL AB.

  To characterize it accurately, You are more familiar with how to set up MySQL.

• Many people know how to run MySQL.

  Again, this is not true for PostgreSQL?

  It actually isn't obvious that, if you drop out the set of people with very shallow understandings, that the relative quantities will differ all that much...

• Some Very Large Web Databases run on MySQL.

  And this may be taken to imply that no large "Web Databases" run on PostgreSQL?

  The largest "Web Database" known is Yahoo's multi-Petabyte database, which is based on PostgreSQL. (It seems to be the largest database of any sort that has been publicly publicized.) It's not exactly PostgreSQL as we know it, but it certainly seems like some form of counterexample, particularly in that this one database probably outweighs the size of all MySQL databases in the world put together...

• Speciality data warehouse engines (e.g., Infobright Brighthouse, Kickfire) have been developed for MySQL.

  Licensing considerations mean that the vendors that have built "specialty DW engines" atop PostgreSQL haven't had to say so. Yahoo's database is certainly an example; ExtenDB, GreenPlum, and Truvisio are others. There is indication (difficult to document, because vendors aren't always declaring themselves) that plenty of vendors out there are using PostgreSQL's parser to connect to other kinds of backends.

  The base capabilities of PostgreSQL are sufficiently interesting that people are using it directly for DW applications; it's only if you've got wackily-large amounts of data, getting to the dozens of terabytes range, where it starts to be necessary to do special things with hardware partitioning.

The only "plus" you can really retain is the "there are a bunch of applications, such as WordPress, specifically coded for MySQL."

Postgresql cons (i have years of exp with MySql and two months exp with Postgres):

• can't do COUNT()-s fast enough.
• can't turn off transactions (to get rid of the overhead)
• requires trick syntax to do multiple inserts in one query
• has no REPLACE INTO
• has no built in backup/replication mechanism
• gets ridiculously huge and slow if not VACUUMed often.
• requires you to list in GROUP BY clause all fields you want to use in SELECT clause, even though you already have primary key listed in GROUP BY.
• requires you to list in SELECT clause all fields you want to use in ORDER BY clause.
• ignores indexes until you manually do ANALYZE
• does not allow to turn off indexes temporarily to accelerate INSERTS and UPDATES
• no support for User-Defined variables (mysql style) that allow doing interesting things in single query, like picking random subset of rows fast:
  SET @toGet=10; SET @left=(SELECT COUNT(*) FROM offers); SELECT *, @toGet:=@toGet-1
  FROM offers WHERE (@left:=@left-1)>0 AND RAND()<@toGet/@left;

From my point of view MySql was just trying to get people what they wanted while PostgreSql was trying to uphold the sql standards, and frankly people like getting what they want.

In most cases db is just a bag to throw data in, and to get them from it very fast. Things Postgres gives you are often unnecessary, and hoops it make you jump through are tiresome.

I also don't like how Postgres is encouraging you to put you logic inside db. You end up with tangled mess where part of logic is inside source files and part is magically enclosed in various triggers, rules and stored procedures in db away from you project and version control system.