Combine Sql Queries

Hello, I have these variables on my page:

userid = "10101"

RequestHost = "example.com"

What would be the best way performace wise to first check if the userid 10101 exists in my sql server db.  If it does exist I would then need to check if "example.com" exists for the userid in the userdomains table.  If these both exist I would then like to query some additional data.  I was hoping its possible to combine this into one query somehow.  I dont think this is the best solution:

 sqlcommand.CommandText = "SELECT UserId From Users Where UserID = '10101'"
Conn.Open()
dr = sqlcommand.ExecuteReader
if dr.hasrows then
sqlcommand2.CommandText = "SELECT UserDomain From UserDomains Where UserID = 'example.com'"
dr2 = sqlcommand2.ExecuteReader
if dr2.hasrows then
sqlcommand3.CommandText = 'Select Additional Data
dr3 = sqlcommand3.ExecuteReader
'read values
conn.close
else
conn.close
'do something
end if
else
conn.close
'do something
end if  Thanks Very Much!