JSP JDBC MySQL 显示表然后将它们选择并联合

Question

我正在尝试显示表格，然后将结果放入 mysql select 语句中。

这里是jsp代码：

<%@ page language="java" import="java.sql.*,java.util.*,java.text.*"%>

    <%
            String DRIVER = "com.mysql.jdbc.Driver";

            Class.forName(DRIVER).newInstance();
            Connection con = null;
            ResultSet rst = null;
            Statement stmt = null;
            Connection con2 = null;
            ResultSet rst2 = null;
            Statement stmt2 = null;     
            try {
                String url = "jdbc:mysql://localhost:3306/mydb?user=root&password=test";
                con = DriverManager.getConnection(url);
                stmt = con.createStatement();
                rst = stmt.executeQuery("select table_name from information_schema.tables where table_schema='mydb' and table_name like '%_work' ");

                con2 = DriverManager.getConnection(url);
                stmt2 = con2.createStatement();
                String table_name="table_name";


                while (rst.next()) {
                    ArrayList<String> list= new ArrayList<String>();

                    list.add(rst.getString("table_name"));  


                    for (String item : list) {                      

                        rst2 = stmt2.executeQuery("select distinct thecolumn from  '"+ item +"'  ");



                    }             
        }
        rst.close();
        stmt.close();
        con.close();
        } 
        catch (SQLException se) {
            //System.out.println("SQL statement is not executed!");
            se.printStackTrace();
        }
        catch (Exception e) {
                System.out.println(e.getMessage());
        }

    %>

我的问题：
请帮助我更正我的代码，使 rst2 变为：

rst2 = stmt2.executeQuery("select distinct thecolumn from  table1_work UNION ALL select distinct thecolumn from  table2_work  UNION ALL select distinct thecolumn from  table3_work" UNION ALL select distinct thecolumn from  tablen_work UNION ALL etc ... ...);

Answer 1

这是一个使用 jstl 的示例：

mySQL.jsp

<%@ page language="java" import="java.sql.*,java.util.*,java.text.*" isELIgnored="false" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%
    String DRIVER = "com.mysql.jdbc.Driver";

    ArrayList<String> tables = new ArrayList<String>();

    Class.forName(DRIVER).newInstance();
    Connection con = null;
    ResultSet rst = null;
    Statement stmt = null;
    Connection con2 = null;
    ResultSet rst2 = null;
    Statement stmt2 = null;     
    try {
        String url = "jdbc:mysql://localhost:3306/mydb?user=root&password=root&useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC";
        con = DriverManager.getConnection(url);
        stmt = con.createStatement();
        rst = stmt.executeQuery("select table_name from information_schema.tables where table_schema='mydb' and table_name like '%_work' ");

        con2 = DriverManager.getConnection(url);
        stmt2 = con2.createStatement();
        String table_name = "table_name";

        //Insert into tables...
        while (rst.next()) {
            tables.add(rst.getString("table_name"));    
        }

        boolean first = true;
        StringBuilder query2 = new StringBuilder();

        //...then iterate over
        for (String table : tables) {           
            if(first) {
              query2.append(" select distinct id from ");
              first = false;
            }else {
              query2.append(" UNION ALL select distinct id from ");
            }
            query2.append('\'').append(table).append('\'');
        }

        //Put variable inside context to access it in jstl
        pageContext.setAttribute("query", query2.toString());
        pageContext.setAttribute("tables", tables);

        rst.close();
        stmt.close();
        con.close();
    } catch (SQLException se) {
        //System.out.println("SQL statement is not executed!");
        se.printStackTrace();
    }
    catch (Exception e) {
        System.out.println(e.getMessage());
    }
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <style>
            table, th, td {
               border: 1px solid black;
            }
        </style>
    </head>
    <body>
        <div>
            <span>Query : ${query}</span>
        </div>
        <table>
            <tr>
              <th>Table name</th>
            </tr>
            <c:forEach var="table" items="${tables}"> 
              <tr>
                <td>
                    <c:out value = "${table}"/>
                </td>
              </tr>
            </c:forEach>
        </table>
    </body>
</html>