[英]How to execute a group of 'select count(*)' queries as a batch in Java?
[英]How can i execute 2 Select Queries in Java?
我正在Eclipse上工作的代码需要您的帮助。 当我尝试执行Java中的2 Select Queries似乎不起作用时,我搜索了Internet,但找不到解决方案。 我需要执行2 select,因为我需要数据库中2个表中的数据。
表1:问题表2:选择
好吧,第一个查询似乎运行良好,因为我可以在执行时按需找到项目。 表2中的项目使我执行“找不到列'selid'。”。 // Selid列在表2。
如果您可以在此方面为我提供帮助,我会在底部将您的错误代码发布到您的网站上。 提前致谢。
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws IOException, ServletException {
//String connectionURL = "jdbc:mysql://127.0.0.1:3306/newData";// newData is the database
//Connection connection;
Connection conn=null;
String dbName="teddb";
res.setContentType("text/html");
res.setCharacterEncoding("utf-8");
PrintWriter out = res.getWriter();
//String dbUserName="root";
//String dbPassword="root";
try{
String qid = "";
String question = "";
String sel1 = "";
String sel2 = "";
String sel3 = "";
String correct = "";
String selid ="";
String sel="";
Connection dbCon;
Class.forName(driver);
dbCon = DriverManager.getConnection(dbURL);
ResultSet rs;
ResultSet rs2;
Statement stmt;
Statement stmt2;
stmt = dbCon.createStatement();
stmt2 = dbCon.createStatement();
String qry = "";
String qry2 = "";
qry = "select * from questions";
qry2 = "select * from selections";
rs = stmt.executeQuery(qry);
stmt = dbCon.prepareStatement(qry);
rs2 = stmt2.executeQuery(qry2);
stmt2 = dbCon.prepareStatement(qry2);
String[] columns = new String[] { "qid",
"question_text" , "selid" , "selection_text" ,};
Random rn = new Random();
int range = 2 - 1 + 1;
int randomNum = rn.nextInt(range) + 1;
out.println(randomNum);
while (rs.next()) {
for (int i = randomNum; i <= randomNum; i++) {
question = rs.getString(columns[1]);
sel1 = rs.getString(columns[2]);
sel2 = rs.getString(columns[3]);
}
}
PreparedStatement pstmt;
for (int z=1;z<=3;z++){
selid = String.valueOf(rs.getString(columns[2]));
pstmt = dbCon.prepareStatement(qry2 + " where qid = ? and selid ='z'");
pstmt.setString(1, qid);
rs2 = pstmt.executeQuery();
while (rs2.next()) {
for (int i = randomNum; i <= randomNum; i++) {
if (z==1)
sel1 = rs.getString(columns[3]);
else if (z==2)
sel2 = rs.getString(columns[3]);
else
sel3 = rs.getString(columns[3]);
}
}
}
out.println("<!DOCTYPE html>"+
"<html><body>"+
"<form method=\"post\" action=\"demoServlet\">"+
"<b><h1>Ερώτηση</h1></b> <br><br>"+
"<b><h1>"+question+" </h1></b> <br><br>"+
"<b> 1: </b> <input type=\"radio\" name=\"iscorrect\" value=\"" + sel1 + "\"/><br>"+
"<b> 2: </b> <input type=\"radio\" name=\"iscorrect\" value=\"" + sel2 + "\"/> <br>"+
"<b> 3: </b> <input type=\"radio\" name = \"iscorrect\" value=\"" + sel3 + "\"/><br><br>"+
"<br><input type=\"submit\" name=\"submit\" value=\"Απάντηση\"/>"+
"</form></body></html>");
dbCon.commit();
String msg=" ";
rs.close();
rs2.close();
stmt.close();
dbCon.close();
}
catch (Exception e){
out.println(e);
}
概念是我有2张桌子,而iam制作了一个表格,用户可以回答一些问题。 我执行两个表,然后尝试使用提交将变量放入表单。 DoPost将在同一Servlet中的DoGet之后生效。
这是表格的示例。
questions | selections
qid | question | qid | | selid | selection_text |correct
q1 | 1+1? | q1 1 5 0
q1 2 2 1 // true
q1 3 4 0
更改
rs = stmt.executeQuery(qry);
rs2 = stmt.executeQuery(qry2);
至
rs = stmt.executeQuery(qry);//first query
rs2 = stmt2.executeQuery(qry2);//second query
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