[wix-users] Installing SQL database

[Phill Hogland]

The confusion that reigns in my mind, probably prevents a coherent question, but I will appreciate any advice.

I have been asked to create some setups (bundle/msi) for a client and server application which shares a database.  The developer/business is not clear on the specification and is asking me basically what is possible.  I have seen several posts about installing SqlExpress.  I downloaded it and started to write a bundle/ ExePackage to do some testing.  I have also done some reading on WixSqlExptension, and am left with some questions.  And I saw Rob's comment here:
http://windows-installer-xml-wix-toolset.687559.n2.nabble.com/Burn-SQL-Express-Install-Fails-0x84b40000-td7391182.html
"PS: When you discover the correct set of parameters, let us know here.
There is a plan afoot to "pre-bake" the silent install of a bunch of well
known redists so you can use them by just doing PackageGroupRef Id="x" at
the correct place in your Chain. "

So if I want to create a SQL db do I just use WixSqlExtenstion and SqlDatabase element or do I also need to install SQLExpress first?
Or do I install SqlExpress and not use SqlDatabase element.  I am not clear on how they relate to each other.

Thanks.
Phill