update inner join

string sql = @"update a 
set a.M_ParentID=b.M_ParentID,
a.M_Name=b.M_Name,
a.M_Seq=b.M_Seq
from SysMenu_BySchool a
inner join (";
foreach (SysMenu_BySchoolEntity m in lstMenu)
{
sql += string.Format("select {0} ID,{1} as M_ParentID,'{2}' as M_Name,{3} as M_Seq union ", m.ID, m.M_ParentID, Utils2.ValidChar(m.M_Name), m.M_Seq);
}
sql = sql.TrimEnd(" union ".ToCharArray());
sql += ") b on a.ID=b.ID";