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

[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);

}