MySQL Java 准备好的语句语法错误

Question

I need to select rows from mysql table based on various criteria, for example Colour= Black, or size= L.

The code works without the preparedstatement and the question marks, but whenever I attempt to use the question marks the code does not run.

I have read something about typing the question mark like \'?'// but I am not sure about the exact format.

String URL = "jdbc:mysql://localhost:3306/clothing";
String USERNAME = "root";
String PASSWORD = "password";
Connection con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
Statement stmt = con.createStatement();
String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ? AND Size = ?;";
ResultSet rs = stmt.executeQuery(sql);
PreparedStatement preparedStmt = con.prepareStatement(sql);
preparedStmt.setString(1, Data1);
preparedStmt.setString(2, Data2);

Also, Size is written out in orange colour, but the error happens also when I only use this sql String

String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ?;";

I have looked at like 20 different answers, but didnt find anything helpful, so thanks in advance for any help!

Answer 1

You are executing the query using a normal java.sql.Statement , not using a java.sql.PreparedStatement . This won't work because a normal Statement does not support parameterized queries. So, remove the creation and execution of the Statement , and make sure you execute the statement using the PreparedStatement :

String URL = "jdbc:mysql://localhost:3306/clothing";
String USERNAME = "root";
String PASSWORD = "password";
String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ? AND Size = ?;";
try (Connection con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
     PreparedStatement preparedStmt = con.prepareStatement(sql)) {
    preparedStmt.setString(1, Data1);
    preparedStmt.setString(2, Data2);
    try (ResultSet rs = preparedStmt.executeQuery()) {
        // process result set
    }
}

Also note the addition of try-with-resources, which will ensure connections, statements and result sets are closed correctly.