InfoPath Dev

How do you reference an InfoPath schema field in an InfoPath data connection SQL select statement ? Can't seem to get the correct syntax.

Here's an example : Would like for the 'u799976' to be an Infopath schema variable.

shape
{select "CostCenterNumber","RoleID","UserID" from "dbo"."Users" WHERE "UserID" = 'u799976'} as "Users"
append
({select "RoleID","RoleTitle" from "dbo"."Role" as "Role"}
relate "RoleID" TO "RoleID") as "Role"

You will probably need to do this with code or rules... Set the query field before querying.