I'm starting the development of a web app with offline database storage requirements. Long story short, the app should be able to run on:
So the question is which technology to choose: IndexedDB or Web SQL Database?
Regarding Web SQL Database, on one hand, it is ready to be used in any of the above scenarios. On the other, Mozilla has stated Firefox will never implement it, and acording to the HTML5 working draft the specification has reached an impasse:
This specification has reached an impasse: all interested implementors have used the same SQL backend (Sqlite), but we need multiple independent implementations to proceed along a standardisation path. Until another implementor is interested in implementing this spec, the description of the SQL dialect has been left as simply a reference to Sqlite, which isn't acceptable for a standard. Should you be an implementor interested in implementing an independent SQL backend, please contact the editor so that he can write a specification for the dialect, thus allowing this specification to move forward.
IndexedDB is the alternative advocated by Mozilla, but it will only come in Firefox 4. Microsoft is interested and Chrome will support it as well. I know nothing of Apple's plans regarding IndexedDB.
I'm personally inclined to choose Web SQL Database, but just because I'm used to SQLite, I like the power and expressiveness of SQL, and I understand the relational model. IndexedDB, for me, is an uncertainty.
That said, I'm afraid of betting on the wrong horse. Is it safe to assume support for Web SQL Database will continue to exist, even if IndexedDB becomes the standard?
(A note on CouchDB: do you also see it as an alternative?)
Considering only WebSQL supports all three requirements you have listed, shouldn't your choice be simple? You have no insight into the development roadmap for Safari or Android, so use what you have available.