MySQL从其他表中选择昵称？

Question

I have 3 tables for a chat app

• chatRooms (id)

• chatMessages (id, roomId, userId, message)

• userData (userId, nickName)

How can I load all the chatRooms with the chatMessages with the nickNames?

I tried:

$qry = $db->prepare('SELECT 
        chatRooms.id,
        chatMessages.message, 
        userData.nickName 
    FROM chatRooms 
    LEFT JOIN chatMessages 
        ON chatMessages.roomId = chatRooms.id 
    LEFT JOIN userData 
        ON chatMessages.userId = userData.userId '
);
$qry->execute();

But it doesn't seem to work for me:C

I would like to display all the users who are in the chatRoom in the chat name

So if 3 people (Fred, Joe, Bane) are in the group then I somehow would need an array with them. For every array element(chatRoom)

Answer 1

Your first LEFT JOIN is more than likely returning more than one row.

From your question, your "chatMessages" table also has a userId in it. You should also filter by this.

In order to do this, you would need to:

1. Join userData before chatMessages

2. Include the userId from userData in the LEFT JOIN on chatMessages

    $qry = $db->prepare('SELECT chatRooms.id, chatMessages.message, userData.nickName FROM chatRooms LEFT JOIN userData ON chatMessages.userId = userData.userId LEFT JOIN chatMessages ON chatMessages.roomId = chatRooms.id AND chatMessages.userId = userData.userId'); $qry->execute();