使用PreparedStatement时com.mysql.jdbc.exceptions.MySQLSyntaxErrorException [英] com.mysql.jdbc.exceptions.MySQLSyntaxErrorException when using PreparedStatement

问题描述

我正在尝试执行一个查询，该查询返回一个名和姓串联在一起的学生，该名与搜索键参数相等.

I am trying to execute a query that returns a student whose name and last name concatenated equal the search key parameter.

为此，我在我的类中执行此操作，该类为我的Student类管理与数据库相关的任何事情.

For that I am doing this in my class that manages anything related to the database for my Student class.

执行查询时，出现以下错误:

When the query is executed I am getting the error that follows:

com.mysql.jdbc.exceptions.MySQLSyntaxErrorException:

怎么了?我已经检查过这是正确的使用方式 concat.

What's wrong? I have checked that's the correct way to use concat.

name和lastName是VARCHAR.

public static Student findStudent(String key) {
    if (key == null) return null;

    PreparedStatement preparedStatement = null;
    ResultSet rs = null;

    String selectSQL = "select * from project.students where concat(name, lastName) = ? ;";

    try {
      dbConnection = getDBConnection();

      preparedStatement = dbConnection.prepareStatement(selectSQL);
      preparedStatement.setString(1, key);

      Student student = null;
      rs = preparedStatement.executeQuery(selectSQL);
      if (rs.next()) {
          StudentDB.setStudentAttributes(student, rs);
      }

      return student;
    } catch(SQLException e) {
      e.printStackTrace();
    } finally {
      close();
      try {
          if (preparedStatement != null) preparedStatement.close();
          if (rs != null) rs.close();
      } catch(SQLException e) {
          e.printStackTrace();
      }
    }
    return null;
}

推荐答案

您的问题是您准备的语句是

Your problem is that you prepare the statement with

preparedStatement = dbConnection.prepareStatement(selectSQL);

这是正确的，但是当您尝试执行PreparedStatement时，再次提供了selectSQL字符串:

which is correct, but then when you try to execute the PreparedStatement you supply the selectSQL string again:

rs = preparedStatement.executeQuery(selectSQL);

那是不正确的.您已经准备好了该语句，因此当需要执行该语句时，您只需

That is incorrect. You've already prepared the statement, so when the time comes to execute it you just do

rs = preparedStatement.executeQuery();

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