sql上下连接例子

sql左右连接例子
String level2id = request.getParameter("srw_level2id");
System.out.println(level2id);
sql左右连接例子
sql = " SELECT ub.id,ub.level2id,ub.weight,ub.memo,ub.questionsid,u.titlename FROM tbquestions u LEFT JOIN tbindexquestions ub on u.id = ub.questionsid WHERE ub.level2id= "+level2id;