Sql错误,当我在JAVA代码中实现join时
我有两张桌子 第一张桌子Sql错误,当我在JAVA代码中实现join时,java,mysql,jsp,jdbc,Java,Mysql,Jsp,Jdbc,我有两张桌子 第一张桌子 Profession带有两个列(Profession\u id,Profession\u name) 第二张桌子 申请人有五个栏(申请人id、专业id、姓、名、入学年份) 表profession中的profession\u id和表profession中的profession\u id是MySQL中的相关字段 我需要的不是职业id,而是可用职业的下拉列表。在这里,我使用内部连接实现 这是我的班级,与DB合作: public enum ApplicantDBProvide
Profession
带有两个列(Profession\u id,Profession\u name)
第二张桌子
申请人
有五个栏(申请人id、专业id、姓、名、入学年份)
表profession
中的profession\u id
和表profession
中的profession\u id
是MySQL中的相关字段
我需要的不是职业id,而是可用职业的下拉列表。在这里,我使用内部连接实现
这是我的班级,与DB合作:
public enum ApplicantDBProvider {
INSTANCE;
private Connection connection;
private ApplicantDBProvider() {
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/db_applicant", "root", "toor");
} catch (ClassNotFoundException | SQLException e) {
System.err.println("Class not found: com.mysql.jdbc.Driver " + e);
throw new RuntimeException("Class not found: com.mysql.jdbc.Driver");
}
}
public Applicant getApplicant(long applicantId) throws Exception {
PreparedStatement preparedStatement = null;
Applicant applicant = null;
try {
preparedStatement = connection.prepareStatement("SELECT * FROM applicant WHERE applicant_id=?");
preparedStatement.setInt(1, (int) applicantId);
ResultSet resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
applicant = new Applicant();
applicant.setId(resultSet.getInt("applicant_id"));
applicant.setFirstName(resultSet.getString("first_name"));
applicant.setLastName(resultSet.getString("last_name"));
applicant.setProfessionId(resultSet.getInt("profession_id"));
applicant.setEntranceYear(resultSet.getInt("entrance_year"));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (preparedStatement != null) {
preparedStatement.close();
}
}
return applicant;
}
public List<Applicant> getApplicants() throws Exception {
Statement statement = null;
List <Applicant> applicants = new ArrayList<>();
try {
statement = connection.createStatement();
//ResultSet resultSet = statement.executeQuery("SELECT * FROM applicant");
ResultSet resultSet = statement.executeQuery("select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name from applicant a join profession p on a.profession_id = p.profession_id");
Applicant applicant = null;
while (resultSet.next()) {
applicant = new Applicant();
applicant.setId(resultSet.getInt("applicant_id"));
applicant.setFirstName(resultSet.getString("first_name"));
applicant.setLastName(resultSet.getString("last_name"));
applicant.setProfessionId(resultSet.getInt("profession_id"));
applicant.setEntranceYear(resultSet.getInt("entrance_year"));
applicants.add(applicant);
}
} catch (SQLException e) {
throw new Exception(e);
}
return applicants;
}
public void saveApplicant(Applicant applicant) throws Exception {
PreparedStatement preparedStatement = null;
try {
if (applicant.getId() == -1) {
preparedStatement = connection.prepareStatement("INSERT INTO applicant (first_name, last_name, profession_id, entrance_year) VALUES (?,?,?,?)");
preparedStatement.setString(1, applicant.getFirstName());
preparedStatement.setString(2, applicant.getLastName());
preparedStatement.setInt(3, (int)applicant.getProfessionId());
preparedStatement.setInt(4, applicant.getEntranceYear());
} else {
preparedStatement = connection.prepareStatement("UPDATE applicant SET first_name=?, last_name=?, profession_id=?, entrance_year=? WHERE applicant_id=?");
preparedStatement.setString(1, applicant.getFirstName());
preparedStatement.setString(2, applicant.getLastName());
preparedStatement.setInt(3, (int) applicant.getProfessionId());
preparedStatement.setInt(4, applicant.getEntranceYear());
preparedStatement.setInt(5, (int) applicant.getId());
}
preparedStatement.executeUpdate();
} catch (SQLException e) {
throw new Exception(e);
} finally {
if (preparedStatement != null) {
preparedStatement.close();
}
}
}
public Profession getProfession(long professionId) throws Exception {
PreparedStatement preparedStatement = null;
Profession profession = null;
try {
preparedStatement = connection.prepareStatement("SELECT * FROM profession WHERE profession_id=?");
preparedStatement.setInt(1, (int) professionId);
ResultSet resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
profession = new Profession();
profession.setId(resultSet.getInt("profession_id"));
profession.setProfessionName(resultSet.getString("profession_name"));
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
if (preparedStatement != null) {
preparedStatement.close();
}
}
return profession;
}
public List<Profession> getProfessions() throws Exception {
Statement statement = null;
List<Profession> professions = new ArrayList<>();
try {
statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery("SELECT * FROM profession");
Profession profession = null;
while (resultSet.next()) {
profession = new Profession();
profession.setId(resultSet.getInt("profession_id"));
profession.setProfessionName(resultSet.getString("profession_name"));
professions.add(profession);
}
} catch (SQLException e) {
throw new Exception(e);
} finally {
if (statement != null) {
statement.close();
}
}
return professions;
}
public void saveProfession(Profession profession) throws Exception {
PreparedStatement preparedStatement = null;
try {
if (profession.getId() == -1) {
preparedStatement = connection.prepareStatement("INSERT INTO profession (profession_name) VALUES (?) ");
preparedStatement.setString(1, profession.getProfessionName());
} else {
preparedStatement = connection.prepareStatement("UPDATE profession SET profession_name=? WHERE profession_id=?");
preparedStatement.setString(1, profession.getProfessionName());
preparedStatement.setInt(2, (int) profession.getId());
}
preparedStatement.executeUpdate();
} catch (SQLException e) {
throw new Exception(e);
} finally {
if (preparedStatement != null) {
preparedStatement.close();
}
}
}
但是,当我运行服务器并打开jsp时,出现了错误:
java.lang.Exception:java.sql.SQLException:未找到“profession\u id”列
我不明白这是一个多么大的错误。可能是什么?请告诉我。谢谢。编辑:
在这个查询中
选择一个申请人id、一个名字、一个姓氏、一个入学年份,
p、 职业名称,p.职业id来自申请人a加入职业p
关于a.profession\u id=p.profession\u id
你只有
a、 申请人id,a.名字,a.姓氏,a.入学年份,
p、 专业名称
没有p.profession\u id
所以当你做一个
applicant.setProfessionId(resultSet.getInt("profession_id"));
您会得到一个异常,因为您的结果列表中没有该列
ResultSet resultSet = statement.executeQuery("select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name, p.profession_id from applicant a join profession p on a.profession_id = p.profession_id");
回答你的问题
我有课。applicator.java。在那门课上,我有一个professionId
具有长数据类型。现在是我的奎斯顿。我什么时候换衣服
申请人.setProfessionId(resultSet.getInt(“profession_id”))在
申请人.setProfessionId(resultSet.getString(“专业名称”)),i
需要将professionId更改为字符串数据类型
您可以向Application.java类添加类变量
作为
而且有两个,
applicant.setProfessionId(resultSet.getInt("profession_id"));
applicant.setProfessionName(resultSet.getString("profession_name"));
但是,
如果你在尝试,我引用
不要获取专业id,而是获取可用的
职业
您应该以不同的方式处理此问题,因为对于一个应用程序
,此联接只会给出一个专业名称
在taglib和数据绑定上有一个战利品
编辑2:发布您的数据库结构,但是,当我在查询中插入“profession\u id”时,结果表中有profession\u id。我需要在结果查询中获取profession\u name。我理解,您建议我更改profession\u name上的profession\u id。但是,我的老师告诉我。它是通过连接来实现的。没有变化@瓦莱里奥解释一下我的老师告诉我的。它是通过连接来实现的。没有变化!对我说:)请回答一个问题!别走!我有课。applicator.java。在那个类中,我有长数据类型的professionId。现在是我的奎斯顿。当我在applicator.setProfessionId(resultSet.getString(“profession\u name”))上更改applicator.setProfessionId(resultSet.getInt(“profession\u id”))时,我需要将professionId更改为字符串数据类型吗?
ResultSet resultSet = statement.executeQuery("select a.applicant_id, a.first_name, a.last_name, a.entrance_year, p.profession_name, p.profession_id from applicant a join profession p on a.profession_id = p.profession_id");
private String professionName;
public String getProfessionName(){
return professionName;
}
public String setProfessionName(String professionName){
this.professionName = professionName
}
applicant.setProfessionId(resultSet.getInt("profession_id"));
applicant.setProfessionName(resultSet.getString("profession_name"));