用mysql查詢在Java中加入兩個數據庫？

Question

我想在java應用程序中運行SQLQuery。 sqlquery連接兩個數據庫（不在同一臺服務器上）。難道更正一下，我在這裏做什麼：

公共功能有：

private DatabaseData externaldb = new DatabaseData("com.mysql.jdbc.Driver", 
"...", "...", "..."); 
    private DatabaseData localdb = new DatabaseData("com.mysql.jdbc.Driver", 
"...", "...", "..."); 
    private Connection externalconnection = null; 
    private Connection localconnection = null; 

    function(externalconnection, c_id, u_d); 

調用的函數是：

private int function(Connection externalconnection, String c_Id, String u_Id) 
    throws SQLException{ 
       String query ="SELECT A.v_id, COUNT(I.v_id) AS v_count " 
         + "FROM externaldb.video_interaction I" 
         + " INNER JOIN localdb.video_additional A ON A.v_id = I.v_id" 
         + " WHERE I.c_id='" + c_id + "' AND I.user'" + u_Id + "';"; 

       Statement stmt = externaldb.createStatement(); 
       ResultSet rs = stmt.executeQuery(query); 

       int counter = 0; 

       if (rs.next()){ 
        counter = rs.getInt("video_count"); 
       } 

       return counter; 

      } 

謝謝！

Answer 1

你有兩個連接，你有兩個數據庫。本地服務器必須能夠訪問本地的外部和外部。然後，創建聯合表格，例如：

CREATE TABLE federated_table (
    id  INT(20) NOT NULL AUTO_INCREMENT, 
    name VARCHAR(32) NOT NULL DEFAULT '', 
    other INT(20) NOT NULL DEFAULT '0', 
    PRIMARY KEY (id), 
    INDEX name (name), 
    INDEX other_key (other) 
) 
ENGINE=FEDERATED 
DEFAULT CHARSET=latin1 
CONNECTION='mysql://fed_user@remote_host:9306/federated/test_table'; 

（從MySQL 5.0.13開始之前，請使用COMMENT而不是CONNECTION）

資料來源：MySQL Cross Server Select Query

更多信息：https://dev.mysql.com/doc/refman/5.7/en/federated-create-server.html