当“WITH”不可用时避免重复子查询

Question

MySQL v5.0.58.

为简洁起见，省略了带有外键约束等的表和其他不相关的细节：

CREATE TABLE `fixture` (
  `id` int(11) NOT NULL auto_increment,
  `competition_id` int(11) NOT NULL,
  `name` varchar(50) NOT NULL,
  `scheduled` datetime default NULL,
  `played` datetime default NULL,
  PRIMARY KEY  (`id`)
);

CREATE TABLE `result` (
  `id` int(11) NOT NULL auto_increment,
  `fixture_id` int(11) NOT NULL,
  `team_id` int(11) NOT NULL,
  `score` int(11) NOT NULL,
  `place` int(11) NOT NULL,
  PRIMARY KEY  (`id`)
);

CREATE TABLE `team` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(50) NOT NULL,
  PRIMARY KEY (`id`)
);

地点：

• 平局会将result.place 设置为0
• result.place 将包含一个整数，表示第一名、第二名等

任务是返回一个字符串，描述给定团队在给定比赛中最近的比赛结果。如果给定的球队获胜，格式应该是“def Team X,Team Y”，如果给定的球队输了，格式应该是“输给 Team X”，如果是平局，格式应该是“与 Team X 打成平手”。是的，理论上每场比赛可能有超过两支球队（尽管 1 对 1 将是最常见的情况）。

这可行，但感觉效率很低：

SELECT CONCAT(
    (SELECT CASE `result`.`place` 
        WHEN 0 THEN "drew with"
        WHEN 1 THEN "def"
        ELSE "lost to"
        END
    FROM `result`
    WHERE `result`.`fixture_id` = 
        (SELECT `fixture`.`id` FROM `fixture`
        LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id`
        WHERE `fixture`.`competition_id` = 2
        AND `result`.`team_id` = 1
        ORDER BY `fixture`.`played` DESC
        LIMIT 1)
    AND `result`.`team_id` = 1),
    ' ',
    (SELECT GROUP_CONCAT(`team`.`name`)
    FROM `fixture`
    LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id`
    LEFT JOIN `team` ON `result`.`team_id` = `team`.`id`
    WHERE `fixture`.`id` = 
        (SELECT `fixture`.`id` FROM `fixture`
        LEFT JOIN `result` ON `result`.`fixture_id` = `fixture`.`id`
        WHERE `fixture`.`competition_id` = 2
        AND `result`.`team_id` = 1
        ORDER BY `fixture`.`played` DESC
        LIMIT 1)
    AND `team`.`id` != 1)
)

我是否遗漏了一些非常明显的事情，或者我不应该尝试在一个查询中执行此操作？还是当前的困难反映了糟糕的桌子设计？

Answer 1

尝试选择您需要的数据（团队名称和目标团队的place），然后将其组合起来。每场比赛两支球队：

SELECT CASE `recent`.`place` 
        WHEN 0 THEN CONCAT("drew with ", other_name)
        WHEN 1 THEN CONCAT("def ", other_name, ", ", targ_name)
        ELSE CONCAT("lost to ", other_name)
    END
FROM (SELECT rtarg.place, targ.name AS targ_name, other.name AS other_name
        FROM `fixture`
        JOIN `result` AS rtarg ON `rtarg`.`fixture_id` = `fixture`.`id`
        JOIN `team` AS targ ON `rtarg`.`team_id` = `targ`.`id`
        JOIN `result` AS rother ON `rother`.`fixture_id` = `fixture`.`id`
        JOIN `team` AS other ON `rother`.`team_id` = `other`.`id`
        WHERE `fixture`.`competition_id` = 2
          AND `rtarg`.`team_id` = @targ
          AND `rother`.`team_id` != @targ
        ORDER BY `fixture`.`played` DESC
        LIMIT 1) AS `recent`;

只需极少改动即可处理每个夹具两个以上的团队，但其他子查询也可以。

SELECT CASE `recent`.`place` 
        WHEN 0 THEN CONCAT("drew with ", other_names)
        WHEN 1 THEN CONCAT("def ", other_names, "; ", targ_name)
        ELSE CONCAT("lost to ", other_names)
    END
FROM (SELECT rtarg.place, targ.name AS targ_name, GROUP_CONCAT(other.name SEPARATOR ', ') AS other_names
        FROM `fixture`
        JOIN `result` AS rtarg ON `rtarg`.`fixture_id` = `fixture`.`id`
        JOIN `team` AS targ ON `rtarg`.`team_id` = `targ`.`id`
        JOIN `result` AS rother ON `rother`.`fixture_id` = `fixture`.`id`
        JOIN `team` AS other ON `rother`.`team_id` = `other`.`id`
        WHERE `fixture`.`competition_id` = 2
          AND `targ`.`id` = @targ
          AND `rother`.`team_id` != @targ
          AND ((rtarg.place<=1 AND rother.place >= rtarg.place)
            OR (rtarg.place>1 AND rother.place < rtarg.place))
        GROUP BY fixture.id
        ORDER BY `fixture`.`played` DESC
        LIMIT 1
) AS recent;

没有指定每场比赛超过两支球队的结果格式，因此可能需要进一步调整。