Question

我有这个相当长的查询，应该给我一些关于货物的信息，它可以工作，但它的表现非常糟糕。加载大约需要4500毫秒。

SELECT
    DATE(paid_at) AS day,
    COUNT(*) as order_count,
    (
      SELECT COUNT(*) FROM line_items
      WHERE order_id IN (SELECT id from orders WHERE DATE(paid_at) = day)
    ) as product_count,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'colissimo'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
    ) as orders_co,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'colissimo'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
      AND paid_amount < 70
    ) as co_less_70,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'colissimo'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
      AND paid_amount >= 70
    ) as co_plus_70,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'mondial_relais'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
    ) as orders_mr,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'mondial_relais'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
      AND paid_amount < 70
    ) as mr_less_70,
    (
      SELECT COUNT(*) FROM orders
      WHERE shipping_method = 'mondial_relais'
      AND DATE(paid_at) = day
      AND state IN ('paid','shipped','completed')
      AND paid_amount >= 70
    ) as mr_plus_70
    FROM orders
    WHERE MONTH(paid_at) = 11
    AND YEAR(paid_at) = 2011
    AND state IN ('paid','shipped','completed')
    GROUP BY day;

知道我可能做错了什么或者我可以做得更好吗？我有其他类似长度的查询，这些查询没有花费太多时间来加载。我认为这比例如每天有一个单独的查询（在我的编程而不是SQL查询中）更快。

Answer 1

您的查询中的问题是一遍又一遍地扫描同一个表。 ORDER表的所有扫描（在您的情况下选择）可以转换为多个SUM + CASE或COUNT + CASE，如SQL query with count and case statement中所示。

Answer 2

这是因为您在不需要它们的情况下使用子查询。

作为一般规则，在主SELECT子句中有子查询的情况下，该子查询将在主SELECT子句中的每一行中查询其中的表一次 - 因此，如果您有7个子查询并且正在选择日期范围为30天，您将有效地运行210个单独的子查询（加上您的主查询）。

（某些查询优化器可以在某些情况下将子查询解析为主查询，但作为一般规则，您不能依赖于此。）

在这种情况下，您不需要任何orders子查询，因为您需要的所有orders数据都包含在主查询中 - 因此您可以将其重写为：< / p>

SELECT
    DATE(paid_at) AS day,
    COUNT(*) as order_count,
    (
      SELECT COUNT(*) FROM line_items
      WHERE order_id IN (SELECT id from orders WHERE DATE(paid_at) = day)
    ) as product_count,
    sum(case when shipping_method = 'colissimo' then 1 end) as orders_co,
    sum(case when shipping_method = 'colissimo' AND 
                  paid_amount < 70 then 1 end) as co_less_70,
    sum(case when shipping_method = 'colissimo' AND 
                  paid_amount >= 70 then 1 end) as co_plus_70,
    sum(case when shipping_method = 'mondial_relais' then 1 end) as orders_mr,
    sum(case when shipping_method = 'mondial_relais' AND 
                  paid_amount < 70 then 1 end) as mr_less_70,
    sum(case when shipping_method = 'mondial_relais' AND 
                  paid_amount >= 70 then 1 end) as mr_plus_70
    FROM orders
    WHERE MONTH(paid_at) = 11
    AND YEAR(paid_at) = 2011
    AND state IN ('paid','shipped','completed')
    GROUP BY day;

子查询执行非常严重的SQL查询

2 个答案: