WebSQL API has been deprecated by W3C and is no longer maintained. Browsers's support may drop in future. I'd highly recommend you switch to better solution like ChotaDB.
I've re-written this plugin from scratch because it is still really popular and most of the browsers are supporting the API.
|Chrome - Desktop|
|Chrome - Mobile|
|Safari - Desktop|
|Safari - iOS|
|Opera - Desktop|
|Opera - Mobile||?|
Detailed support is available here.
More detail, demo and docs can be found at http://moin.im/plugins/webdb/index.html