在 Mysql where 子句中使用 java 变量

Question

我想在 SQL 中使用 java 变量 syntax.Please 建议是否可能 not.Here 是我的代码

String Userid_input=request.getParameter("Userid");//I am getting dynamic input from User

String Password_input=request.getParameter("Password");

下面给出数据库连接

Class.forName("com.mysql.jdbc.Driver");
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/Proj_name","root","root");
Statement st=con.createStatement();
ResultSet rs=st.executeQuery("select User_type from Signup where User_name.User_name=Userid_input");//**Userid_input** is a java variable

我收到以下错误，

发生异常 com.mysql.jdbc.exceptions.MySQLSyntaxErrorException：'where clause'

中的未知列 'Userid_input'

Answer 1

试试这个：

ResultSet rs=st.executeQuery("select User_type from Signup where User_name=" + Userid_input);

Answer 2

试试这个，

   String query = "select User_type from Signup where User_name.User_name="+Userid_input;
   ResultSet rs = st.executeQuery(query);

参考：https://docs.oracle.com/javase/tutorial/jdbc/basics/retrieving.html

Answer 3

或者，您可以使用准备好的语句：

String query = "SELECT User_type FROM Signup WHERE User_name.User_name = ?";

PreparedStatement ps = conn.prepareStatement(query);

ps.setInt(1, Userid_input);

ResultSet rs = ps.executeQuery();

有关准备好的语句的更多信息http://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html

在 Mysql where 子句中使用 java 变量

Using java variables in Mysql where clause

java

mysql

resultset