如何加速与子查询关联的更新查询

Question

我有一个非常包含LEFT JOIN子查询的查询。完全加载需要20分钟。

这是我的问题：

UPDATE orders AS o

LEFT JOIN (
    SELECT obe_order_master_id, COUNT(id) AS count_files, id, added
    FROM customer_instalments 
    GROUP BY obe_order_master_id
) AS oci ON oci.obe_order_master_id = SUBSTRING(o.order_id, 4)

SET o.final_customer_file_id = oci.id,
    o.client_work_delivered  = oci.added

WHERE oci.count_files = 1

有什么方法可以让这个查询运行得更快？

Answer 1

在Temp Table中移动Where条件并将WHERE替换为HAVING子句，这将从临时表中删除不必要的行，因此减少过滤并可能有助于提高性能

UPDATE orders AS o
LEFT JOIN (
   SELECT obe_order_master_id, id, added
   FROM customer_instalments 
   GROUP BY obe_order_master_id
   HAVING COUNT(id) = 1 
) AS oci ON oci.obe_order_master_id = SUBSTRING(o.order_id, 4)
SET o.final_customer_file_id = oci.id,
    o.client_work_delivered  = oci.added

Answer 2

我建议为Order_id substring创建单独的列并在其上创建索引。然后在WHERE中使用此列。