Just the small list of flaws that we hit trying to use mysql (there's dozens more, and we're not including all the "mysql silently inserts invalid data" gotchas):

no check constraints

views with aggregates are too slow to be used

no expression indexes

triggers don't fire on cascaded actions

no window functions

can't set default values to be the result of a function

no transactional DDL

doesn't have multiple databases, just schemas misnamed as databases

rollbacks are orders of magnitude slower than other RDBMS, and if it is interrupted it can corrupt the database

functions can't use prepare/execute, so no dynamic SQL in functions

subqueries are broken: can't modify and select from the same table

functions can't be called recursively (seriously? is this 1962?)

triggers can't alter the table they are firing against

stored procedures can't be invoked from prepare/execute

"slow query" log has a completely useless resolution of seconds