Admin: 1 версия

2010-06-01T05:06:31Z

1 версия

в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Designated column"s table name ==



<source lang="java">
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);
}
}</source>



== Get column names of a table using ResultSetMetaData ==



<source lang="java">
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);
}
}
}
}</source>



== Get column"s precision and scale value ==



<source lang="java">
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);
}
}</source>



== If a table column can have a null value or not ==



<source lang="java">
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");
}
}
}</source>

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Admin: 1 версия

в 17:44, 31 мая 2010