使用 HAVING 子句的慢查询 - 我可以加快速度吗？

Question

我有以下查询产生了预期的结果，但速度很慢（大约需要 10 秒。gstats table 在我的开发环境中有大约 130k 行，在生产环境中要大得多）：

SELECT count(d.id) AS dcount, s.id, s.name
FROM sites s
LEFT JOIN deals d ON (s.id = d.site_id AND d.is_active = 1)
WHERE (s.is_active = 1)
AND s.id IN(
    SELECT g.site_id
    FROM gstats g
    WHERE g.start_date > '2015-04-30'
    GROUP BY g.site_id
    HAVING SUM(g.results) > 100
)
GROUP BY s.id
ORDER BY dcount ASC

我是不是做错了什么？我怎样才能加快速度？

添加 indexes/using 视图会有帮助吗？

Answer 1

快速解决方法是在子查询中使用 filter：

SELECT count(d.id) AS dcount, s.id, s.name
FROM sites s
LEFT JOIN deals d ON (s.id = d.site_id AND d.is_active = 1)
WHERE (s.is_active = 1)
AND s.id IN(
    SELECT g.site_id
    FROM gstats g
    WHERE g.start_date > '2015-04-30'<b> AND g.site_id = s.id</b>
    GROUP BY g.site_id
    HAVING SUM(g.results) > 100
)
GROUP BY s.id
ORDER BY dcount ASC

否则，您将对每个可能的候选人进行这样的分组查询。我们可以用 EXISTS:

让它更优雅

SELECT count(d.id) AS dcount, s.id, s.name
FROM sites s
LEFT JOIN deals d ON (s.id = d.site_id AND d.is_active = 1)
WHERE (s.is_active = 1)
AND <b>EXISTS (
    SELECT 1
    FROM gstats g
    WHERE g.site_id = s.id AND g.start_date > '2015-04-30'
    HAVING SUM(g.results) > 100
)</b>
GROUP BY s.id
ORDER BY dcount ASC

但我们还没有完成，现在我们将为每个元素使用 EXISTS。这很奇怪，因为查询只依赖于 s.id，所以它只依赖于 group，而不是单独的行。因此可能加速，但这取决于表的大小等，是将条件移动到 HAVING 语句：

SELECT count(d.id) AS dcount, s.id, s.name
FROM sites s
LEFT JOIN deals d ON (s.id = d.site_id AND d.is_active = 1)
WHERE (s.is_active = 1)
GROUP BY s.id
ORDER BY dcount ASC
<b>HAVING</b> EXISTS (
    SELECT 1
    FROM gstats g
    WHERE g.site_id = s.id AND g.start_date > '2015-04-30'
    HAVING SUM(g.results) > 100
)

Answer 2

尝试将子查询移动到 FROM 子句：

SELECT count(d.id) AS dcount, s.id, s.name
FROM sites s JOIN
     (SELECT g.site_id
      FROM gstats g
      WHERE g.start_date > '2015-04-30'
      GROUP BY g.site_id
      HAVING SUM(g.results) > 100
     ) g
     ON g.site_id = s.site_id LEFT JOIN
     deals d
     ON s.id = d.site_id AND d.is_active = 1
WHERE s.is_active = 1
GROUP BY s.id
ORDER BY dcount ASC;

我假设您在 join 列上有索引。您可能还会发现这有助于提高性能：

SELECT s.id, s.name,
       (SELECT COUNT(*)
        FROM deals d
        WHERE d.site_id = s.id AND d.is_active = 1
       ) as dcount
FROM sites s JOIN
     (SELECT g.site_id
      FROM gstats g
      WHERE g.start_date > '2015-04-30'
      GROUP BY g.site_id
      HAVING SUM(g.results) > 100
     ) g
     ON g.site_id = s.site_id 
WHERE s.is_active = 1
ORDER BY dcount ASC;

对于此版本，您需要 deals(site_id, is_active) 上的索引。

Answer 3

查询看起来很好。我建议以下索引：

create index idx_gstats on gstats(start_date, results, site_id);
create index idx_deals1 on deals(is_active, site_id);
create index idx_deals2 on deals(site_id, is_active);

然后查看查询的执行计划并删除未使用的交易索引。

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