更新存储过程中的 table 记录和 return 该记录的 ID

Question

在 2 位玩家的 Android 文字游戏中 -

游戏数据保存在以下table:

# desc games;
+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| gid      | int(11)      | NO   | PRI | NULL    | auto_increment |
| created  | int(11)      | NO   |     | NULL    |                |
| player1  | int(11)      | YES  |     | NULL    |                |
| player2  | int(11)      | YES  |     | NULL    |                |
| stamp1   | int(11)      | NO   |     | NULL    |                |
| stamp2   | int(11)      | NO   |     | NULL    |                |
| letters1 | varchar(7)   | NO   |     | NULL    |                |
| letters2 | varchar(7)   | NO   |     | NULL    |                |
| letters  | varchar(116) | NO   |     | NULL    |                |
| board    | varchar(225) | NO   |     | NULL    |                |
| style    | int(11)      | NO   |     | 0       |                |
+----------+--------------+------+-----+---------+----------------+

player1 和 player2 列保留了一场比赛中对方玩家的 2 个不同数字 ID。

stamp1 和 stamp2 是最后一步的时间戳（最初为 0）。

我正在尝试编写一个 stored procedure，它将带一个玩家 uid 并加入一个只有 1 个其他玩家的空游戏，或者从头开始创建一个新游戏。

一个特殊情况是：如果已经有玩家 uid 的新游戏并且她还没有执行任何动作（即 stamp1 是 0)，然后我只是 return 该游戏的 gid（而不是创建另一个新游戏）。

delimiter $$$

drop procedure if exists find_game;
create procedure find_game(IN uid integer,
                           IN letters1 varchar(7),
                           IN letters2 varchar(7),
                           IN letters varchar(116),
                           OUT gid integer)
begin
        start transaction;

        /* maybe there is a new game already, just waiting for the player's 1st move*/
        select gid into @gid from games where (player1 = uid and stamp1 = 0) or (player2 = uid and stamp2 = 0) limit 1;

        IF found_rows() = 0 THEN
                /* try to find games having just 1 player (with different uid) */
                update games set player2 = uid where player1 != uid and stamp1 > 0 and player2 = null;
                IF row_count() = 0 THEN
                        /* create new game with player1 = uid and stamp1 = 0*/
                        insert into games (created, player1, stamp1, stamp2, letters1, letters2, letters, board, style)
                        values (unix_timestamp(), uid, 0, 0, letters1, letters2, letters, space(225), 1);
                ELSE
                        /* how to find the gid of the updated record? */
                END IF;
        END IF;

        commit;
end
$$$

不幸的是，上面的代码有两个问题。

1) 如果我评论除上面第一个 select 语句之外的所有内容 - 我在 [=50 中得到 null =]gid，而当我 运行 在 mysql 提示时它按预期工作：

# select gid from games where (player1 = 1 and stamp1 = 0) or (player2 = 1 and stamp2 = 0);
+-----+
| gid |
+-----+
|   1 |
|   2 |
|   3 |
+-----+

2)请指教，如何在上述row_count() > 0的情况下找到更新游戏的gid。或者有更好的方法吗？

更新

我听从了 Juan Carlos 的建议（谢谢！），我尝试使用以下代码首先 select 然后 update:

delimiter $$$

drop procedure if exists find_game;
create procedure find_game(IN uid integer,
                           IN letters1 varchar(7),
                           IN letters2 varchar(7),
                           IN letters varchar(116),
                           OUT gid integer)
begin
        start transaction;

        /* maybe there is a new game already, just waiting for the player's 1st move*/
        select gid into @gid from games
        where (player1 = uid and stamp1 = 0) or (player2 = uid and stamp2 = 0) limit 1;

        IF select found_rows() = 0 THEN
                /* try to find games having just 1 player (with different uid) */
                select gid into @gid from games
                where (player1 != uid and stamp1 > 0 and player2 is null) limit 1;

                IF select found_rows() > 0 THEN
                        update games set player2 = uid where gid = @gid;
                ELSE
                        /* create new game with player1 = uid and stamp1 = 0*/
                        insert into games (created, player1, stamp1, stamp2, letters1, letters2, letters, board, style)
                        values (unix_timestamp(), uid, 0, 0, letters1, letters2, letters, space(225), 1);

                        select last_insert_id() into @gid;
                END IF;
        END IF;

        commit;
end
$$$

不幸的是，我收到语法错误：

ERROR 1064 (42000): 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 
'select found_rows() = 0 THEN

                select gid into @g' at line 13

Answer 1

如果你已经有这个，但是如果玩家已经在一个全新的游戏中，这会发现。

 select gid into @gid 
 from games 
 where (player1 != uid and stamp1 = 0) 
    or (player2 = uid and stamp2 = 0) limit 1;

为什么不使用类似的东西更改您的更新，您可以在其中寻找有空位的游戏。

 select gid into @gid 
 from games 
 where (player1 !=  uid and stamp1 > 0 and player2 is null);

 update games set player2 = uid where gid = @gid 

注意： 为什么要搜索 stamp1 > 0??您的插入创建了 stamp1 = 0 的新游戏，您的更新不会找到仅 1 player

的游戏