Java Tutorial/Database/Column

Designated column"s table name

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class Main {
  private static final String DRIVER = "com.mysql.jdbc.Driver";
  private static final String URL = "jdbc:mysql://localhost/testdb";
  private static final String USERNAME = "root";
  private static final String PASSWORD = "";
  public static void main(String[] args) throws Exception {
    Class.forName(DRIVER);
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
    Statement statement = connection.createStatement();
    String query = "SELECT a.id, a.username, a.country_id, b.country_name " + "FROM users a "
        + "LEFT JOIN countries b ON a.country_id = b.id";
    ResultSet resultSet = statement.executeQuery(query);
    ResultSetMetaData metadata = resultSet.getMetaData();
    String tableName = metadata.getTableName(1);
    System.out.println("Table name of column "id" = " + tableName);
    tableName = metadata.getTableName(4);
    System.out.println("Table name of column "country name" = " + tableName);
  }
}

Get column names of a table using ResultSetMetaData

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
import java.util.ArrayList;
public class Main {
  private static final String DRIVER = "com.mysql.jdbc.Driver";
  private static final String URL = "jdbc:mysql://localhost/testdb";
  private static final String USERNAME = "root";
  private static final String PASSWORD = "";
  public static void main(String[] args) throws Exception {
    Class.forName(DRIVER);
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT * FROM users");
    ResultSetMetaData metadata = resultSet.getMetaData();
    int columnCount = metadata.getColumnCount();
    ArrayList<String> columns = new ArrayList<String>();
    for (int i = 1; i < columnCount; i++) {
      String columnName = metadata.getColumnName(i);
      columns.add(columnName);
    }
    while (resultSet.next()) {
      for (String columnName : columns) {
        String value = resultSet.getString(columnName);
        System.out.println(columnName + " = " + value);
      }
    }
  }
}

Get column"s precision and scale value

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class Main {
  private static final String DRIVER = "com.mysql.jdbc.Driver";
  private static final String URL = "jdbc:mysql://localhost/testdb";
  private static final String USERNAME = "root";
  private static final String PASSWORD = "";
  public static void main(String[] args) throws Exception {
    Class.forName(DRIVER);
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
    Statement statement = connection.createStatement();
    String query = "SELECT stock_id, name, price FROM stocks";
    ResultSet resultSet = statement.executeQuery(query);
    ResultSetMetaData metadata = resultSet.getMetaData();
    int precision = metadata.getPrecision(3);
    int scale = metadata.getScale(3);
    System.out.println("Precision: " + precision);
    System.out.println("Scale    : " + scale);
  }
}

If a table column can have a null value or not

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
public class Main {
  private static final String DRIVER = "com.mysql.jdbc.Driver";
  private static final String URL = "jdbc:mysql://localhost/testdb";
  private static final String USERNAME = "root";
  private static final String PASSWORD = "";
  public static void main(String[] args) throws Exception {
    Class.forName(DRIVER);
    Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT id, username FROM users");
    ResultSetMetaData metadata = resultSet.getMetaData();
    int nullability = metadata.isNullable(1);
    if (nullability == ResultSetMetaData.columnNullable) {
      System.out.println("Columns ID can have a null value");
    } else if (nullability == ResultSetMetaData.columnNoNulls) {
      System.out.println("Columns ID does not allowed to have a null value");
    } else if (nullability == ResultSetMetaData.columnNullableUnknown) {
      System.out.println("Nullability unknown");
    }
  }
}