T-SQL (transact-SQL) valid in SQLite and other SQL databases?
T-SQL is Microsoft's implementation (dialect) of the ANSI SQL standard. Like most implementations, there are portions that are proprietary and not standard, quirks that are permissible but not idiomatic for other platforms, and items defined in the standard that are not implemented. MySQL, sqlite, and others are the same way, and so sometimes a quirk with another platform will make "correct" and standards-compliant T-SQL be broken for that platform.
In other words, if you know T-SQL, you know about 85% of what you need to write queries for SQLite, MySQL, oracle, db2, Informix, Access, etc. However, there will be a few bumps; definitely don't expect code written for one platform to work on another.
CASE is one of those instances where the various flavors of sql tend to differ, with a number of other implementations choosing a syntax based on IF instead. The core SELECT, FROM, WHERE keywords, on the other hand, tend to be more consistent.