如何提高SQL查询多个连接表的性能

Question

我如何提高性能这个查询，同时还获得所需的所有信息..

SELECT 
    tr.id, tr.request_status, tr.note, tr.created_date, 
    c.name AS customer_name, c.mobile_phONe, 
    u.full_name AS created_by_name, tt.name AS ticket_type_name 
FROM 
    ticket_request tr 
LEFT JOIN 
    ticket_type tt ON tt.id = tr.ticket_type_id 
LEFT JOIN 
    users u ON u.id = tr.created_by 
LEFT JOIN 
    customer c ON c.id = tr.customer_id 
WHERE 
    tr.is_deleted != 1 
    AND tr.user_id IN (SELECT u.id FROM users u WHERE u.status = '1') 
GROUP BY 
    tr.id 
ORDER BY 
    tr.created_date DESC 
LIMIT 0,20 

目前，该查询在7-10秒内运行。

• ticket_request表有大约10万行
• customers表有300K左右行
• users表ticket_type没有那么多（约1K行）

Answer 1

下面的加速技术是免除LIMIT第一个，只有在那之后，再做所有的JOINs。

SELECT tr3.id, tr3.request_status, tr3.note, tr3.created_date, 
     c.name AS customer_name, c.mobile_phONe, 
     u2.full_name AS created_by_name, 
     tt.name AS ticket_type_name 
    FROM 
    (
     SELECT tr1.id 
      FROM ticket_request tr1 
      JOIN users u1 ON u1.id = tr1.created_by 
      WHERE u1.status = '1' 
       AND tr1.is_deleted != 1 
      ORDER BY tr1.created_date DESC 
      LIMIT 0,20 
    ) AS tr2 
    JOIN ticket_request AS tr3 ON tr3.id = tr2.id 
    JOIN user AS u2 ON u2.id = tr3.created_by 
    LEFT JOIN ticket_type tt ON tt.id = tr3.ticket_type_id 
    LEFT JOIN customer c ON c.id = tr3.customer_id 
    ORDER BY tr3.created_date 

的JOINs，所述一个中的 “衍生自” 表TR2，都在触摸只有20行之后;这是加速的很大一部分。

这可能是一样好：

SELECT d.id, d.request_status, d.note, d.created_date, 
     c.name AS customer_name, c.mobile_phONe, d.created_by_name, 
     tt.name AS ticket_type_name 
    FROM 
    (
     SELECT tr.id AS tr_id, tr.request_status, tr.note, tr.created_date, 
       tr.ticket_type_id, tr.customer_id 
       u.full_name AS created_by_name 
      FROM ticket_request tr 
      JOIN users u ON u.id = tr.created_by 
      WHERE u.status = '1' 
       AND tr.is_deleted != 1 
      ORDER BY tr.created_date DESC 
      LIMIT 0,20 
    ) AS d 
    LEFT JOIN ticket_type tt ON tt.id = d.ticket_type_id 
    LEFT JOIN customer c ON c.id = d.customer_id 
    ORDER BY d.created_date 

Answer 2

我假设你正在使用MySQL。如果不是，这个答案可以稍微修改以适应另一个数据库，但这个概念应该保持不变。您ticket_request表之间

ALTER TABLE ticket_type ADD INDEX (id); 
ALTER TABLE users ADD INDEX (id); 
ALTER TABLE customer ADD INDEX (id);  -- important 

要解释为什么指数会有所帮助，考虑第一LEFT JOIN：您可以添加索引，其涉及您的左边的右边与ticket_request列加入所有的ID列ticket_type表。如果没有索引，对于ticket_request中的每条记录，数据库将不得不扫描整个ticket_type表以查找与连接条件相匹配的记录。从性能角度来看，这是昂贵的。但是对于索引，数据库可以更快地完成此操作，因为它“知道”匹配记录的准确位置（或几乎完全匹配）。

虽然您提到只有customer表非常大，但您仍可以将索引添加到其他表中。未来，他们可能会变得更大。涉及customer的加入很可能是您查询中的瓶颈。

Answer 3

这里的优化最大的机会是LIMIT 0,20

1. ​​是没有意义的，应予删除。

2. create index ticket_request_ix_is_deleted_created_date on ticket_request (is_deleted,created_date) and change tr.is_deleted != 1 to tr.is_deleted = 0。

   或者

   create index ticket_request_ix_created_date on ticket_request (created_date)

Answer 4

SELECT 
    tr.id, tr.request_status, tr.note, tr.created_date, 
    c.name AS customer_name, c.mobile_phONe, 
    u.full_name AS created_by_name, tt.name AS ticket_type_name 
FROM 
    ticket_request tr 
LEFT JOIN 
    ticket_type tt ON tt.id = tr.ticket_type_id and tr.is_deleted != 1 
LEFT JOIN 
    users u ON u.id = tr.created_by 
JOIN 
    users u1 ON u1.id = tr.user_id and u1.status = '1' 
LEFT JOIN 
    customer c ON c.id = tr.customer_id 
GROUP BY 
    tr.id 
ORDER BY 
    tr.created_date DESC 
LIMIT 0,20 

尝试这一点，将与更好的性能工作，调整为按您的要求

Answer 5

比索引其他，在应用层上可以使用的Memcached（如果你使用PHP）喜欢的东西。这也会给你很好的表现。