多个select写在一起？？

Question

sql="select * from user_topic where topic_id=(select max(topic_id) from user_topic where username='"+session.getAttribute("username")+"')";
改成
sql="select * from user_topic,(select max(topic_id) as maxtopic_id from user_topic where username='"+session.getAttribute("username")+"')" A where topic_id=A.maxtopic_id;

Answer 1

楼主的SQL语句没什么问题吧！

Answer 2

出这个错误啊！ cricketlj(蟋蟀) 的也是一样出错！应该不关SQL语句的事吧？
那是那里有错啊？org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
root cause java.lang.NullPointerException
org.apache.jsp.bbs_002dindex_jsp._jspService(bbs_002dindex_jsp.java:205)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856

Answer 3

执行这个SQL语句就出错，不执行没错！

Answer 4

是不是mysql用户权限的问题？？