列不在“从Java数据库搜索”列表中的任何表中
我正在用Java开发一个数据库程序,它告诉我我要搜索的内容不在表中,我遇到了一个问题列不在“从Java数据库搜索”列表中的任何表中,java,sql,database,Java,Sql,Database,我正在用Java开发一个数据库程序,它告诉我我要搜索的内容不在表中,我遇到了一个问题 public static void displayRecord(ResultSet rs) throws SQLException { String assignment = rs.getString("assignment"); int grade = rs.getInt("grade"); System.out.println(assignment + " | " + grade
public static void displayRecord(ResultSet rs) throws SQLException
{
String assignment = rs.getString("assignment");
int grade = rs.getInt("grade");
System.out.println(assignment + " | " + grade + "\n");
}
public void findGrade(String assignment){
String assignString;
int gradeInt;
try{
Class.forName(driver).newInstance();
}
catch (Exception err){
System.err.println("Unable to load the embedded driver.");
err.printStackTrace(System.err);
System.exit(0);
}
Connection connected = null;
try{
int ble = 25;
connected = DriverManager.getConnection(protocol + databaseName);
Statement statement = connected.createStatement();
ResultSet rs = null;
rs = statement.executeQuery("SELECT assignment, grade FROM student WHERE assignment = " + assignment);
if(rs == null ) {
System.out.println("Assignment not found!");
}
else {
displayRecord(rs);
}
rs.close();
connected.close();
}
catch (SQLException err){
System.err.println("SQL error.");
err.printStackTrace(System.err);
System.exit(0);
}
}
它最终给了我以下错误
SQL错误。
java.sql.SQLSyntaxErrorException:列“ASSIGNMENT1”不在FROM列表中的任何表中,或者出现在联接规范中,并且不在联接规范的范围内,或者出现在HAVING子句中,并且不在GROUP BY列表中。如果这是CREATE或ALTER TABLE语句,则“ASSIGNMENT1”不是目标表中的列。
位于org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(未知源)
位于org.apache.derby.impl.jdbc.Util.generateCsSQLException(未知源)
位于org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(未知源)
位于org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(未知源)
位于org.apache.derby.impl.jdbc.EmbedConnection.handleException(未知源)
位于org.apache.derby.impl.jdbc.ConnectionChild.handleException(未知源)
位于org.apache.derby.impl.jdbc.EmbedStatement.execute(未知源代码)
位于org.apache.derby.impl.jdbc.EmbeddeStatement.executeQuery(未知源代码)
在Student.findGrade(Student.java:153)
在GradeBookTester.main(GradeBookTester.java:17)
我不确定它为什么会给我数据库中存在的错误
我将为测试人员和数据库创建者自己提供代码,以查看是否存在错误,但这一切看起来都非常可靠
数据库:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class CreateGradeBook{
private static final String driver = "org.apache.derby.jdbc.EmbeddedDriver";
private static final String protocol = "jdbc:derby:";
public static void main(String[] args)
{
try{
Class.forName(driver).newInstance();
System.out.println("Loaded the embedded driver.");
}
catch (Exception err){
System.err.println("Unable to load the embedded driver.");
err.printStackTrace(System.err);
System.exit(0);
}
String dbName = "GradeBook";
Connection connected = null;
try{
System.out.println("connecting to and creating the database...");
connected = DriverManager.getConnection(protocol + dbName + ";create=true");
System.out.println("database created.");
Statement statement = connected.createStatement();
statement.execute("CREATE TABLE student" + "(student_name varchar(50), student_id int, assignment varchar(80), grade int)");
System.out.println("created Student table.");
connected.close();
}
catch (SQLException err){
System.err.println("SQL error.");
err.printStackTrace(System.err);
System.exit(0);
}
}
}
这是测试仪的代码
public class GradeBookTester {
public static void main(String[] args) {
Student bob = new Student();
bob.setStudentName("Bob");
bob.setStudnetID(12345);
bob.addGrade("ASSIGNMENT1", 100);
bob.addGrade("assignment2", 50);
bob.addGrade("assignment3", 25);
bob.addGrade("assignment4", 100);
bob.displayGrades();
bob.findGrade("ASSIGNMENT1");
}
}
您必须使用如下引号提及搜索字符串
rs = statement.executeQuery("SELECT assignment, grade FROM student WHERE assignment = '" + assignment + "'");
问题是您的查询得到如下解释,选择作业,从作业=作业1 而不是 选择作业,从作业='ASSIGNMENT1'所在的学生处评分
让查询解释器将其视为一个列而不是一个值啊,好吧,是的,这很有道理,真不敢相信我错过了。非常感谢你!您的问题准备工作非常好,但决不要在代码中使用显式sql来防止sql注入的危险。改用过程调用。