MySQL - checking if column exists if not create it in Java

Question

I've spent a few hours researching on how to create a Java method that will help with my program. I am very new to MySQL, so I am not the most experienced person out there.

What I am trying to do is write a Java method that checks if a column that has the is named after a username exists inside of a table. If it does not exists, it will create that column.

I have seen lot's of tutorials on the internet about similar solutions to my problem. I don't see how I am supposed to implement the TABLE_SCHEMA into a java method since I only know the very basics of MySql.

It would be nice to see how to implement this or some other solution into the Java method. I've mostly erased my previous work since I could not figure it out, so sorry if I need to show that(This is my first question.)

Edit:

        try {
        ResultSet res = conn.createStatement()
                .executeQuery("ALTER TABLE `package_table` ADD " + username + "  VARCHAR(15);");
        if (!res.next()) {
            conn.createStatement()
                    .executeUpdate("INSERT INTO `package_table` (`uuid`, `name`, `packages`) VALUE ('"
                            + event.getPlayer().getUniqueId() + "', '" + event.getPlayer().getName() + "', '" + "" + "');");
        }
    } catch (SQLException e) {
        e.printStackTrace();
        try {
            conn.close();
        } catch (SQLException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }

Edit2: The reason I need to do columns is that I need to store the 'packages' a username has. There can be "infinite" amounts of packages.

Thanks, Jack

Answer 1

You can do it using jdbc. Just get column names and then add one if you need.

Something like this:

Connection con;
Statement st;
ResultSet rs;

try {
  Class.forName("com.mysql.jdbc.Driver");
  con = DriverManager.getConnection(
      "jdbc:mysql://localhost:3306/dbname",
      "dbuser",
      "bdpass"
  );

  st = con.createStatement();

  String sql = "select * from table";
  rs = st.executeQuery(sql);
  ResultSetMetaData metaData = rs.getMetaData();
  int rowCount = metaData.getColumnCount();

  boolean isMyColumnPresent = false;
  String myColumnName = "myColumnName";
  for (int i = 1; i <= rowCount; i++) {
    if (myColumnName.equals(metaData.getColumnName(i))) {
      isMyColumnPresent = true;
    }
  }

  if (!isMyColumnPresent) {
    String myColumnType = "some type";
    st.executeUpdate("ALTER TABLE table ADD " + myColumnName + " " + myColumnType);
  }
} catch (Exception e) {
  e.printStackTrace();
}

Answer 2

You can do something like this,

DatabaseMetaData  metadata = conn.getMetaData();
Resultset rs = null; 
  rs=metadata.getColumns(null, null, "package_table", null);
boolean found=false;

         while (rs.next()) {

               if(username.equals(rs.getString("COLUMN_NAME"))
              {
              found=true;
              }                       

             } 

       if(found){
       //Skip column creation    
       }else{
       //Create column
      }