The one that you are currently using is the best one to learn. They're all different and they all work slightly differently. You need to learn generalities, not specifics, until you're working with a specific RDBMS.
SQLite is fine. The biggest issue to be aware of with SQLite is that SQLite's type affinity system is completely different from how other SQL RDBMSs function. The norm is for columns to have much more rigid data typing.
SQLite is fine. The biggest issue to be aware of with SQLite is that SQLite's type affinity system is completely different from how other SQL RDBMSs function. The norm is for columns to have much more rigid data typing.