Sharepoint SPQuery vs SPSiteDataQuery

Sharepoint SPQuery vs SPSiteDataQuery
The SPQuery class is used to build query strings to filter or retrieve the specific set of data programmatically from a SP List object.
Syntax: SPQuery query = new SPQuery();
query.Query = <Where><Eq><FieldRef Name= “colname”/><Value type=”text”>filter parameter</value></Eq></Where>;
SPSiteDataQuery is used for cross-site and cross-list searching. SPSiteDataQuery can be used to search in all lists of a particular list type or list base type located in either the complete site collection or a particular site and sub-sites.
SPSiteDataQuery query = new SPSiteDataQuery();
query .ViewFields = “<FieldRef Name=”Title”/>”;
query .Lists = “<Lists ServerTemplate=”101″/>”;
query .Webs = “<Webs Scope=”SiteCollection”/>”;
query .Query = “<Where>” +
“<Contains>” +
“<FieldRef Name=”Title”/>” +
“<Value Type=”Text”>Conditional Parameter </Value>” +
“</Contains>” +
“</Where>”;
SPSite site = new SPSite(http://SP2010);
SPWeb web = site.OpenWeb();
DataTable dt = web.GetSiteData(query);
dt.Rows[0]["Title"]);
Points To Remember
Eq = Equal.
NEq= not equal conditions.
FieldRef Keeps the column name on which we want to apply the query.
Value Keeps the parameter for the query column.
We can use / before column name with / tags to have the corresponding NULL condition checks.