三个连接的查询非常慢

Question

我正在尝试返回所有在特定date 中拥有足球matches 的国家/地区。数据定义在下表中：

比赛

id | country_id | name 
50       1         Premier League

competition_seasons

id | competition_id | name
 70       50          2019

competition_rounds

id | season_id | name 
 58       70      Regular Season

匹配

id | round_id | home | away | result | datetime
 44      58       22     87     1 - 0  2019-03-16:00:00

competition表中存储了不同的比赛，那么每个比赛可以有多个season存储在competition_seasons中。一个season也可以有不同的竞争rounds，这些都存储在competition_rounds中。

所有matches 都存储在match 表中，并为round_id 分组。

我为 API 编写了这个方法：

$app->get('/country/get_countries/{date}', function (Request $request, Response $response, array $args)
{
  $start_date = $args["date"] . " 00:00";
  $end_date = $args["date"] . " 23:59";

  $sql = $this->db->query("SELECT n.* FROM country n
    LEFT JOIN competition c ON c.country_id = n.id
    LEFT JOIN competition_seasons s ON s.competition_id = c.id
    LEFT JOIN competition_rounds r ON r.season_id = s.id
    LEFT JOIN `match` m ON m.round_id = r.id
    WHERE m.datetime BETWEEN '" . $start_date . "' AND '" . $end_date . "'
    GROUP BY n.id");

  $sql->execute();
  $countries = $sql->fetchAll();
  return $response->withJson($countries);
});

有上千条按id组织的记录，但是查询大约需要6、7秒才能返回所有在指定日期播放的countries。

如何优化这个过程？

性能

更新

如果我注意到了一件有趣的事情：

SELECT round_id, DATE("2019-03-18") FROM `match`

查询速度非常快，所以我猜datetime 字段会减慢连接部分的速度，你知道吗？

表结构

CREATE TABLE IF NOT EXISTS `swp`.`competition` (
  `id` INT NOT NULL,
  `country_id` INT NULL,
  `name` VARCHAR(255) NULL,
  `category` INT NULL,
  PRIMARY KEY (`id`),
  INDEX `id_idx` (`country_id` ASC),
  INDEX `FK_competition_types_competition_type_id_idx` (`category` ASC),
  CONSTRAINT `FK_country_competition_country_id`
    FOREIGN KEY (`country_id`)
    REFERENCES `swp`.`country` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_competition_categories_competition_category_id`
    FOREIGN KEY (`category`)
    REFERENCES `swp`.`competition_categories` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;


CREATE TABLE IF NOT EXISTS `swp`.`competition_seasons` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `competition_id` INT NOT NULL,
  `season_id` INT NULL,
  `name` VARCHAR(45) NOT NULL,
  `update_at` DATETIME NULL,
  PRIMARY KEY (`id`),
  INDEX `FK_competition_competition_seasons_competition_id_idx` (`competition_id` ASC),
  CONSTRAINT `FK_competition_competition_seasons_competition_id`
    FOREIGN KEY (`competition_id`)
    REFERENCES `swp`.`competition` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

CREATE TABLE IF NOT EXISTS `swp`.`competition_rounds` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `round_id` INT NULL,
  `season_id` INT NOT NULL,
  `name` VARCHAR(255) NULL,
  PRIMARY KEY (`id`),
  INDEX `FK_competition_seasons_competition_rounds_season_id_idx` (`season_id` ASC),
  CONSTRAINT `FK_competition_seasons_competition_rounds_season_id`
    FOREIGN KEY (`season_id`)
    REFERENCES `swp`.`competition_seasons` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

-- -----------------------------------------------------
-- Table `swp`.`match`
-- -----------------------------------------------------
CREATE TABLE IF NOT EXISTS `swp`.`match` (
  `id` INT NOT NULL,
  `round_id` INT NOT NULL,
  `group_id` INT NULL,
  `datetime` DATETIME NULL,
  `status` INT NULL,
  `gameweek` INT NULL,
  `home_team_id` INT NULL,
  `home_team_half_time_score` INT NULL,
  `home_team_score` INT NULL,
  `home_extra_time` INT NULL,
  `home_penalties` INT NULL,
  `away_team_id` INT NULL,
  `away_team_half_time_score` INT NULL,
  `away_team_score` INT NULL,
  `away_extra_time` INT NULL,
  `away_penalties` INT NULL,
  `venue_id` INT NULL,
  `venue_attendance` INT NULL,
  `aggregate_match_id` INT NULL,
  PRIMARY KEY (`id`),
  INDEX `home_team_id_idx` (`home_team_id` ASC),
  INDEX `away_team_id_idx` (`away_team_id` ASC),
  INDEX `venue_id_idx` (`venue_id` ASC),
  INDEX `match_status_id_idx` (`status` ASC),
  INDEX `FK_competition_rounds_match_round_id_idx` (`round_id` ASC),
  INDEX `FK_match_match_aggregate_match_id_idx` (`aggregate_match_id` ASC),
  INDEX `FK_competition_groups_match_group_id_idx` (`group_id` ASC),
  CONSTRAINT `FK_team_match_home_team_id`
    FOREIGN KEY (`home_team_id`)
    REFERENCES `swp`.`team` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_team_match_away_team_id`
    FOREIGN KEY (`away_team_id`)
    REFERENCES `swp`.`team` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_venue_match_venue_id`
    FOREIGN KEY (`venue_id`)
    REFERENCES `swp`.`venue` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_match_status_match_status_id`
    FOREIGN KEY (`status`)
    REFERENCES `swp`.`match_status` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_competition_rounds_match_round_id`
    FOREIGN KEY (`round_id`)
    REFERENCES `swp`.`competition_rounds` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_match_match_aggregate_match_id`
    FOREIGN KEY (`aggregate_match_id`)
    REFERENCES `swp`.`match` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `FK_competition_groups_match_group_id`
    FOREIGN KEY (`group_id`)
    REFERENCES `swp`.`competition_groups` (`id`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;

Answer 1

首先，将查询写成：

SELECT n.*
FROM country n JOIN
     competition c
     ON c.country_id = n.id JOIN
     competition_seasons s
     ON s.competition_id = c.id JOIN
     competition_rounds r
     ON r.season_id = s.id JOIN
     `match` m
     ON m.round_id = r.id
WHERE m.datetime >= ? AND
      m.datetime < ?
GROUP BY n.id;

此处的更改相对较小，不会影响性能。但它们很重要：

• JOIN 而不是 LEFT JOIN，因为您要求条件匹配。
• 日期参数而不是修改查询字符串，因为这是个好主意。
• >= 和 < 用于比较，因为这适用于日期和日期时间。您需要在结束日期上增加 1 天，但不要使用时间部分。

然后，为了性能，您需要索引：

• match(datetime, round_id)
• competition_rounds(id, season_id)
• competition_seasons(id, competition_id)
• competition(id, country_id)
• country(id)

其实第一个是最重要的。如果将各自的 id 列声明为主键，则不需要最后四个。

Answer 2

使用LEFT JOIN，查询只能从上到下执行，这意味着扫描最后一个表以查找前表中条目的每个产品。此外，在没有任何聚合的情况下使用 LEFT JOIN 和 GROUP BY 是没有意义的，因为它总是会返回所有国家/地区 ID。话虽如此，我会这样重写它：

SELECT DISTINCT
    c.country_id
FROM 
    competition c,
WHERE 

    EXISTS (
        SELECT 
            *
        FROM
            competition_seasons s,
            competition_rounds r,
            `match` m
        WHERE
            s.competition_id = c.id
            AND r.season_id = s.id
            AND m.round_id = r.id 
            AND m.datetime BETWEEN ...
    )

这将被我所知道的所有 RDB 正确优化。 请注意，(match.datetime, match.round_id) 上的 2 列索引 - 按此顺序，将对性能产生巨大影响。或者是写入速度是一个问题，建议至少在(match.datetime) 上使用单列索引。

关于字符串索引的重要说明：字符串比较在 RDB 中总是很奇怪。确保对日期时间列使用二进制排序规则或使用本机 DATETIME 格式。各种 RDB 可能无法在不区分大小写的列上使用索引。

请注意，我删除了 n 上的连接 - 只需添加另一个 PK 查找来检查国家/地区是否仍然存在于国家/地区表中。如果您没有任何 ON DELETE CASCADE 或其他确保数据一致性的约束，您可以将其重新添加，如下所示：

SELECT DISTINCT
    n.id
FROM 
    country n
WHERE 

    EXISTS (
        SELECT 
            *
        FROM
            competition c,
            competition_seasons s,
            competition_rounds r,
            `match` m
        WHERE
            c.country_id=n.id
            AND s.competition_id = c.id
            AND r.season_id = s.id
            AND m.round_id = r.id 
            AND m.datetime BETWEEN ...
    )