下面是一个存储过程（XAMPP〉phpMyAdmin）：

DROP PROCEDURE IF EXISTS changeTurn;

        DELIMITER //

        create procedure changeTurn(in currentGameID bigint(20))
        begin
            declare turnHasBeenChanged tinyint(1) default 0

            select @targetPlayer := player_number from game_players where gameID = currentGameID and current_turn = 1

            set @targetPlayer = @targetPlayer + 1

            update game_players set current_turn = 0 where gameID = currentGameID and current_turn = 1

            while turnHasBeenChanged = 0 do
                case
                    when @targetPlayer > 4
                    then set @targetPlayer = 1
                end
                case
                    when (select forfeit_next_turn from game_players where gameID = currentGameID and player_number = @targetPlayer) = 1
                    then
                    update game_players set forfeit_next_turn = 0 where gameID = currentGameID and player_number = @targetPlayer
                    set @targetPlayer = @targetPlayer + 1
                    else
                    update game_players set current_turn = 1 where gameID = currentGameID and player_number = @targetPlayer
                    set turnHasBeenChanged = 1
                end
            end while
        end

        end //
        DELIMITER ;

无论是否使用分隔符，我都遇到以下问题：

# 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'select @targetPlayer := player_number from game_players where gameID = curren...' at line 5

不幸的是，这并不是很具体。
当把这个过程拼凑在一起的时候，我确保我对每一部分都使用了正确的语法。但是现在，它完全被破坏了。请你给予我一些指导，说明为什么会出错？
我检查了第4行（declare turnHasBeenChanged tinyint（1）default 0），以防它的语法导致后续行失败，并在它的末尾添加了一个分号，这在该行中断了它，所以它不是这样。
然后，我对照https://www.oreilly.com/library/view/mysql-cookbook/0596001452/ch01s15.html验证了第5行的语法，它似乎是正确的......？