Question

我正在尝试让我的代码顺利运行但是在第一次插入之后，当表存在时，我总是在创建fisr表并插入数据后出现此错误com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Table 'bus' already exists此错误发生？！我想只检查表是否存在，如果没有创建tabe并插入数据，如果是，只需更新数据。

数据库类：

package org.busTracker.serverSide;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Database {

    public void connection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("jar works :) ");

        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void insertData(String mac, int route, float latitude,
            float longitude) {

        connection();
        String host = "jdbc:mysql://localhost/busTracker";
        String user = "root";
        String password = "";

        try {
            Connection con = DriverManager.getConnection(host, user, password);

            // Create a statement
            Statement stt = con.createStatement();

            // Check whether table exists.
            boolean rest = stt.execute("SHOW TABLES like 'bus' ");

            if (rest) {

                PreparedStatement prep = con
                        .prepareStatement("REPLACE INTO bus(mac, route, latitude, longitude)"
                                + "VALUES( ?, ?, ? , ? )");
                prep.setString(1, mac);
                prep.setInt(2, route);
                prep.setFloat(3, latitude);
                prep.setFloat(4, longitude);
                prep.executeQuery();

            } else {

                // Create bus table
                stt.execute("CREATE TABLE bus"
                        + "(id INT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,"
                        + "mac VARCHAR(30) NOT NULL UNIQUE,"
                        + "route int(11) NOT NULL,"
                        + "latitude FLOAT(10,6) NOT NULL,"
                        + "longitude FLOAT(10,6) NOT NULL,"
                        + "created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP)");

                PreparedStatement prep = con
                        .prepareStatement("REPLACE INTO bus(mac, route, latitude, longitude)"
                                + "VALUES( ?, ?, ? , ? )");
                prep.setString(1, mac);
                prep.setInt(2, route);
                prep.setFloat(3, latitude);
                prep.setFloat(4, longitude);
                prep.executeQuery();

            }

        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

Answer 1

您可能希望使用CREATE TABLE IF NOT EXISTS语法

https://dev.mysql.com/doc/refman/5.5/en/create-table.html

这样可以避免这种错误

但我会检查是否

{{1}}

正常工作，您可能会得到错误的结果并执行错误的操作

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException：表'总线'已经存在

1 个答案: