http://sqlrelay.sourceforge.net/index.html
It has a native TCL API and supports most popular databases.
One problem: It doesn't have production ready support to run against databases on Windows, but for the lucky people who use Linux/Unix, it seems to be an excellent solution, while TDBC is being developed.
The TCL part of the db connection will work just fine on Windows connecting to sqlrelay running on Linux/Unix (which, in turn, can connect to the database running on Windows :) ). What it doesn't have is production ready support (according to developers) for sqlrelay running on Windows.
bjdev - 2021-09-17 08:22:42
I've spent some weeks testing Sqlrelay. Some parts of the API don't work (for example proc getColumnIsPrimaryKeyByIndex {col} , proc getColumnIsPartOfKeyByIndex {col} ). I sent multiple emails to the support address advertised on the website, but didn't get a response to any of my queries (perhaps the developer has too much on).
I also tried the equivalent calls in PHP and Python and they didn't work either. Which at least shows that it isn't just the Tcl API.
Still, in my testing so far, most of it is working. One of the things that wasn't clear (to me) from the documentation is that calls like proc getTableList {wild} and proc getColumnList {table wild} return a result set over which one must iterate. The wildcard char is SQL's "%" character.