How to write 'select * from table where condtion' query

Question

[ToolboxItemAttribute(false)]

    public class AssignedToMeResults : CoreResultsWebPart

    {

        protected override XPathNavigator GetXPathNavigator(string viewPath)

        {

            // SPContext.Current.Web.CurrentUser.LoginName => "SHAREPOINT\\system"

            // SPContext.Current.Web.CurrentUser.Name => "System Account"

            // Read active AD User Name who logged in

            string adUserName = Page.User.Identity.Name;

            string[] fullName = adUserName.Split('\\');

            string domainName = string.Empty;

            string userName = string.Empty;

            if (fullName.Length == 2)

            {

                domainName = fullName[0];

                userName = fullName[1];

            }

            // Restrict the actual result and look for the property where user name is not

            QueryManager queryManager = SharedQueryManager.GetInstance(this.Page).QueryManager;

            queryManager.UserQuery = "FirstName:Peter";

            //queryManager.UserQuery = "SELECT FirstName FROM Scope() WHERE \"scope\" = 'All Sites'";\

                      

            return base.GetXPathNavigator(viewPath);

        }

    }