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mysql - 在jsp中将数据库表显示为rankingtable

转载 作者：行者123 更新时间：2023-11-29 22:36:09 25 4
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我需要实现一个数据库查询，它可以返回玩家的用户名、分数和排名。由于我没有直接存储在数据库中的排名，所以我必须通过玩家的分数来计算它。

有一个我不明白的 SQL 语法错误。

有人可以告诉我如何使用 java servlet 进行数据库连接。并在jsp中显示结果。

我使用 MySql 5.6.21 和 Tomcat 7。

有人可以帮我吗？

现在我在回溯中收到一个新错误，我确信这是因为准备好的语句是错误的，但我该如何修复它。对于我来说，在 java servlet 中执行此操作会更容易，但我需要直接在此页面上获得结果。

排名.jsp

    <!DOCTYPE html>
<html lang="en">
<%@ page import="java.io.*,java.util.*,java.sql.*"%>
<%@ page import="javax.servlet.http.*,javax.servlet.*" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql"%>

<head>

    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <meta name="description" content="">
    <meta name="author" content="Nicolas Almy">

    <title>Sweep-It | Ranking</title>

    <!-- Custom CSS -->
    <link href="css/screen.css" rel="stylesheet">

    <!-- Bootstrap Core CSS -->
    <link href="css/bootstrap.min.css" rel="stylesheet">

    <!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.2/jquery.min.js"></script>

     <!-- Bootstrap Core JavaScript -->
    <script src="js/bootstrap.min.js"></script>

    <!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
    <!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
    <!--[if lt IE 9]>
        <script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script>
        <script src="https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js"></script>
    <![endif]-->

</head>

<body>

    <!-- Navigation -->
    <div id="navbar-outer">
        <nav class="navbar navbar-inverse" role="navigation">
            <div class="container-fluid">
                <div class="navbar-header">
                  <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#navbar">
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span>
                    <span class="icon-bar"></span> 
                  </button>
                </div>
                <div class="collapse navbar-collapse" id="navbar">
                    <ul class="nav navbar-nav">
                        <li>
                            <a href="index.html">Home</a>
                        </li>
                        <li>
                            <a href="ranking.jsp">Ranking</a>
                        </li>
                        <li>
                            <a href="howtoplay.html">How to play</a>
                        </li>
                        <li>
                            <a href="aboutus.html">About us</a>
                        </li>
                  </ul>
                  <!--  
                  <ul class="nav navbar-nav navbar-right">
                    <li><a href="#"><span class="glyphicon glyphicon-user"></span> Register</a></li>
                    <li><a href="#"><span class="glyphicon glyphicon-log-in"></span> Login</a></li>
                  </ul> -->
                </div>
            </div>
        </nav>
    </div>
    <!-- Page Content -->
    <div class="container">
        <div class="row">
            <div class="col-sm-12" id="welcome-text">
                <div class="box">
                    <p class="box-text">On this page you can see which ones are the top players at the moment. If you are logged in you can see your own statics.</p>

                    <!-- SELECT * from user Order by rating DESC; -->
                    <sql:setDataSource var="snapshot" driver="com.mysql.jdbc.Driver"
                         url="jdbc:mysql://localhost:3306/sweepit"
                         user="root"  password="AbA011"
                    />

                    <c:set var="prevValue" value="NULL" />
                    <c:set var="rankCount" value="0" />

                    <sql:query dataSource="${snapshot}" var="result">       

                    SELECT UserId, Rating, Username, 
                    CASE
                        WHEN prevValue = Rating THEN rankCount
                        WHEN prevValue = Rating THEN rankCount = rankCount + 1
                    END AS rank
                    FROM user
                    ORDER BY Rating

                    <sql:param value="$prevalue" />
                    <sql:param value="$rankCount" />

                    </sql:query>

                    <div id="table-div">     
                        <table id="table-ranking" border="1" >
                            <tr>
                                <th>Rank</th>
                                <th>Username</th>
                                <th>Score</th>
                            </tr>
                            <c:forEach var="row" items="${result.rows}">
                                <tr class="box-text">                   
                                    <td><c:out value="${row.rank}"/></td>
                                    <td><c:out value="${row.username}"/></td>
                                    <td><c:out value="${row.rating}"/></td>   
                                </tr>
                            </c:forEach>
                        </table>
                    </div>
                </div>
            </div>
        </div>
        <!-- /.row -->

    </div>
    <!-- /.container -->

</body>

</html>

用户.sql

create table `User` (
    `UserId` int auto_increment NOT NULL,
    `Username` varchar(25) NOT NULL,
    `RegistrationDate` datetime NOT NULL DEFAULT NOW(),
    `Email` varchar(50) NOT NULL,
    `Authorization` enum('Admin', 'Default', 'Guest') NOT NULL,
    `Rating` int NOT NULL DEFAULT 0,
    `Password` varchar(32) NOT NULL,
    PRIMARY KEY (`UserId`)
) ENGINE=InnoDB AUTO_INCREMENT=1000 DEFAULT CHARSET=UTF8;

错误的堆栈跟踪

  Apr 10, 2015 8:58:56 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/sweepit] threw exception [javax.servlet.ServletException: javax.servlet.jsp.JspException:        

                    SELECT UserId, Rating, Username, 
                    CASE
                        WHEN prevValue = Rating THEN rankCount
                        WHEN prevValue = Rating THEN rankCount = rankCount + 1
                    END AS rank
                    FROM user
                    ORDER BY Rating




                    : Parameter index out of range (1 > number of parameters, which is 0).] with root cause
java.sql.SQLException: Parameter index out of range (1 > number of parameters, which is 0).
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1075)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:984)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:929)
    at com.mysql.jdbc.PreparedStatement.checkBounds(PreparedStatement.java:3711)
    at com.mysql.jdbc.PreparedStatement.setInternal(PreparedStatement.java:3695)
    at com.mysql.jdbc.PreparedStatement.setString(PreparedStatement.java:4546)
    at com.mysql.jdbc.PreparedStatement.setObject(PreparedStatement.java:3950)
    at org.apache.taglibs.standard.tag.common.sql.QueryTagSupport.setParameters(QueryTagSupport.java:304)
    at org.apache.taglibs.standard.tag.common.sql.QueryTagSupport.doEndTag(QueryTagSupport.java:223)
    at org.apache.jsp.ranking_jsp._jspx_meth_sql_005fquery_005f0(ranking_jsp.java:352)
    at org.apache.jsp.ranking_jsp._jspService(ranking_jsp.java:184)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

最佳答案

您忘记了 SQL 查询中 Username 和 CASE 之间的逗号。

                SELECT UserId, Rating, Username,
                CASE
                    WHEN prevValue = Rating THEN rankCount 
                    WHEN prevValue := Rating THEN rankCount := rankCount + 1
                END AS rank
                FROM user
                ORDER BY Rating

关于mysql - 在jsp中将数据库表显示为rankingtable，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29541071/

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