The performance characteristics of `char` vs. `varchar` vs. `text` certainly depends on the implementation details of each RDBMS. PostgreSQL recommends that you

The performance characteristics of `char` vs. `varchar` vs. `text` certainly depends on the implementation details of each RDBMS. PostgreSQL recommends that you use `text` for basically every textual column, but other databases can be very different. Some won't even allow you to add an index to a `text` column. The various timestamp-related data types are also very PostgreSQL-specific.