java - 使用内连接将多个 sql 查询转为单个查询

Question

我有这个java代码:

ArrayList<MessageMap> ids = getNewMail(UserID, type, maxIdMessage);
Message[] message = new Message[ids.size()];
if(ids.size()>0){
   ResultSet rs;
   int j =0;
   for(MappaMessaggi i : ids){
      pstmt = conn.prepareStatement("SELECT * FROM Messaggi WHERE MessageID = ?");
      pstmt.setInt(1, i.getMessageID());
      rs = pstmt.executeQuery();
      rs.next();
      .
      .
      .
   }

其中 getNewMail 是:

public synchronized ArrayList<MessageMap> getNewMail(int UserID,int type,int max){
   ArrayList<MessageMap> map = new ArrayList<MessageMap>();
   try {
      pstmt = conn.prepareStatement("SELECT * FROM MessageMap WHERE UserID = ? AND TipoID = ? AND MessageID > ?");
      .
      .//fill arraylist with resultSet 
      .
}

我知道只需一个查询就可以做同样的事情，但我不知道如何..有人可以睁开我的眼睛吗？ :)谢谢!!!

编辑:我尝试:

SELECT i.*
FROM Messaggi AS i
INNER JOIN MessageMap AS p i.MessageID = p.MessageID
WHERE p.MessageID = 1 AND p.UserID = 1 AND p.TipoID = 2

但我检索到:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'i.MessageID = p.MessageID WHERE p.MessageID = 1 AND p.UserID = 1 AND p.TipoID = ' at line 3

Answer 1

试试这个:

SELECT i.*, p.*
FROM Messaggi i
INNER JOIN MessageMap p ON i.MessageID = p.MessageID
WHERE i.MessageID = ? AND p.UserID = ? AND p.TipoID = ?