Having a mySQL error, unknown column where clause [duplicate]

问题

I am currently having a problem selecting a certain item from a mySQL database. My program is designed to pass a parameter from an android application to a servlet which then queries the database.

However an error appears on the console window: Unknown column '0102310c24' in 'where clause'

There is only an error when the value I want to select contains a letter.

When I query this number 0106172459, the data I want is returned without a problem.

Below is my servlet.

import java.io.*;
import java.util.*;
import javax.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DBServlet extends HttpServlet {
public void service(HttpServletRequest request,HttpServletResponse response)
throws IOException, ServletException{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String x=request.getParameter("item");
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
con =DriverManager.getConnection ("jdbc:mysql://IP/databasename", "username", "password");
stmt = con.createStatement();
rs = stmt.executeQuery("SELECT * FROM items WHERE item="+x);
// displaying records
while(rs.next()){
out.print(rs.getObject(1).toString());
out.print(",");
out.print(rs.getObject(2).toString());
out.print(",");
out.print(rs.getObject(3).toString());
out.print(",");
out.print(rs.getObject(4).toString());
out.print(",");
out.print(rs.getObject(5).toString());
out.print(",");
out.print(rs.getObject(6).toString());
out.print(",");
out.print(rs.getObject(7).toString());
out.print(",");
out.print(rs.getObject(8).toString());
out.print(",");
out.print("\n");
}
} catch (SQLException e) {
throw new ServletException("Servlet Could not display records.", e);
} catch (ClassNotFoundException e) {
throw new ServletException("JDBC Driver not found.", e);
} finally {
try {
if(rs != null) {
rs.close();
rs = null;
}
if(stmt != null) {
stmt.close();
stmt = null;
}
if(con != null) {
con.close();
con = null;
}
} catch (SQLException e) {}
}
out.close();
}
}

and I use this to send the value to the servlet.

List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>();
nameValuePair.add(new BasicNameValuePair("item","List<NameValuePair> nameValuePair = new ArrayList<NameValuePair>();
nameValuePair.add(new BasicNameValuePair("item","010238a2cc"));"));

I will be thankful if anyone could help

回答1:

The value x should be enclosed in quotes, or a non-numeric value would be assumed to refer to a column rather than a string literal.

rs = stmt.executeQuery("SELECT * FROM items WHERE item='"+x + "'");

Note that your script appears to be vulnerable to SQL injection, as the value x has not been escaped but was received from the Request. It would be better to use a prepared statement here.

回答2:

Try to use PreparedStatement.

PreparedStatement st = con.prepareStatement("SELECT * FROM items WHERE item=?");
st.setString(1,x);
rs = st.executeQuery();

回答3:

If the item is of String type, then you need to enclose it in quotes. Better yet, you should use a PreparedStatement, to execute the query.

回答4:

If value x is integer then use the following code:- rs = stmt.executeQuery("SELECT * FROM items WHERE item="+x); If value x is string then use the following code:- rs = stmt.executeQuery("SELECT * FROM items WHERE item=' "+x" ' ");

来源：https://stackoverflow.com/questions/9192781/having-a-mysql-error-unknown-column-where-clause

标签

java

android

mysql

servlets