我试图检索分页列表和＆＃34;通知的总数＆＃34;关于＆＃34;案例＆＃34;属于特定用户。
通知有一些条件是＆＃34;没有锁定＆＃34;，＆＃34;不是私人＆＃34;，＆＃34;还没有看到＆＃34;并且应该返回＃found，然后按创建日期降序排序。
最后一个条件是用户自己没有创建通知，或者通知属于＆＃34;行为＆＃34; （枚举）和user_id在通知中引用＆＃34; ref_id＆＃34;
此查询需要5秒以上的时间才能在recent_changes中运行200k行，在cases和50位用户中运行少于4k行。
+-----+
| cnt |
+-----+
| 13 |
+-----+
1 row in set (4.67 sec)
此查询可以自行优化，还是需要重组？
SELECT count(*) as cnt
FROM recent_changes rc
LEFT JOIN `case` c on c.id = rc.case_id
LEFT JOIN `user` u on u.id = rc.user_id
WHERE
(
rc.user_id != c.user_id AND c.user_id = '25'
OR
(rc.type = 'conduct' AND rc.ref_id = '25')
)
AND c.locked = 'N' AND rc.private != 'Y'
AND seen = 'false'
ORDER BY rc.datecreated DESC;
解释输出
+----+-------------+-------+--------+--------------------------+-------------------------+---------+--------------------------+------+------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+--------------------------+-------------------------+---------+--------------------------+------+------------------------------+
| 1 | SIMPLE | c | ALL | PRIMARY,user_user_id_idx | NULL | NULL | NULL | 3699 | Using where; Using temporary |
| 1 | SIMPLE | rc | ref | idx_recent_changes_case | idx_recent_changes_case | 5 | xxxxxxxxxxxxx.c.id | 25 | Using where |
| 1 | SIMPLE | u | eq_ref | PRIMARY | PRIMARY | 4 | xxxxxxxxxxxxx.rc.user_id | 1 | Using index |
+----+-------------+-------+--------+--------------------------+-------------------------+---------+--------------------------+------+------------------------------+
recent_changes的索引：
+----------------+------------+------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+----------------+------------+------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| recent_changes | 0 | PRIMARY | 1 | id | A | 182807 | NULL | NULL | | BTREE | |
| recent_changes | 1 | recent_changes_user_id_idx | 1 | user_id | A | 96 | NULL | NULL | YES | BTREE | |
| recent_changes | 1 | idx_recent_changes_user_case | 1 | user_id | A | 92 | NULL | NULL | YES | BTREE | |
| recent_changes | 1 | idx_recent_changes_user_case | 2 | case_id | A | 18280 | NULL | NULL | YES | BTREE | |
| recent_changes | 1 | idx_recent_changes_case | 1 | case_id | A | 7312 | NULL | NULL | YES | BTREE | |
+----------------+------------+------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
case表上的索引：
+-------+------------+------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+
| case | 0 | PRIMARY | 1 | id | A | 3753 | NULL | NULL | | BTREE | |
| case | 1 | id_idx | 1 | member_id | A | 3753 | NULL | NULL | YES | BTREE | |
| case | 1 | user_user_id_idx | 1 | user_id | A | 2 | NULL | NULL | YES | BTREE | |
| case | 1 | case_ha_id | 1 | health_authority_id | A | 28 | NULL | NULL | YES | BTREE | |
+-------+------------+------------------+--------------+---------------------+-----------+-------------+----------+--------+------+------------+---------+
它在概念中做了以下几点：
在recent_changes中查找最近的行：
i）recent_changes行通过case_id加入case表，该表由当前user_id拥有
ii）并且当前user_id
OR
i）recent_changes行是＆＃34;行为＆＃34; type和当前user_id位于recent_changes.ref_id列
中如果我删除＆＃34; OR（rc.type =＆＃39;行为＆＃39; AND rc.ref_id =＆＃39; 25＆＃39;）＆＃34;条件然后我得到＆lt; 1s响应时间。
如果我删除＆＃34; rc.user_id！= c.user_id AND c.user_id =＆＃39; 25＆＃39; OR＆＃34;条件仍然需要大约5秒才能完成。
修改
虽然我无法在case。case_id上rc加入rc，但我已加入SELECT count(*) as cnt
FROM `user` u
LEFT JOIN `recent_changes` rc on u.id = rc.user_id
LEFT JOIN `case` c on c.id = rc.case_id
WHERE
(
rc.user_id != c.user_id AND c.user_id = '25'
OR
(rc.type = 'conduct' AND rc.ref_id = '25')
)
AND c.locked = 'N' AND rc.private != 'Y'
AND seen = 'false'
ORDER BY rc.datecreated DESC;
首先加入select count(*) as cnt
FROM (
SELECT count(*) FROM `user` u
LEFT JOIN `recent_changes` rc on u.id = rc.user_id
LEFT JOIN `case` c on c.id = rc.case_id
WHERE rc.user_id != c.user_id AND c.user_id = '25'
AND c.locked = 'N' AND rc.private != 'Y'
AND seen = 'false'
UNION ALL
SELECT count(*) as cnt
FROM `user` u
LEFT JOIN `recent_changes` rc on u.id = rc.user_id
LEFT JOIN `case` c on c.id = rc.case_id
WHERE rc.type = 'conduct' AND rc.ref_id = '25'
AND c.locked = 'N' AND rc.private != 'Y'
AND seen = 'false') x
专栏＆＃39; rc.user_id＆＃39;在＆＃39; where子句＆＃39;。
新查询：
rc删除＆＃34; ORDER BY＆＃34;虽然我现在更了解它的性能影响，但似乎并没有增加新的连接顺序查询。
使用UNION并不是更快，但单独运行每个选择指出第一个SELECT只需要.3s，其中第二个选择超过4s：
EXPLAIN SELECT count(*) FROM `user` u LEFT JOIN `recent_changes` rc on u.id = rc.user_id LEFT JOIN `case` c on c.id = rc.case_id WHERE rc.user_id != c.user_id AND c.user_id = '25' AND c.locked = 'N' AND rc.private != 'Y' AND seen = 'false';
我认为recent_changes +----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
| 1 | SIMPLE | c | ref | PRIMARY,user_user_id_idx | user_user_id_idx | 5 | const | 383 | Using where |
| 1 | SIMPLE | rc | ref | recent_changes_user_id_idx,idx_recent_changes_user_case,idx_recent_changes_case | idx_recent_changes_case | 5 | hsaedmp_jason.c.id | 20 | Using where |
| 1 | SIMPLE | u | eq_ref | PRIMARY | PRIMARY | 4 | hsaedmp_jason.rc.user_id | 1 | Using index |
+----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
表格根据EXPLAIN没有必要的索引：
EXPLAIN SELECT count(*) as cnt FROM `user` u LEFT JOIN `recent_changes` rc on u.id = rc.user_id LEFT JOIN `case` c on c.id = rc.case_id WHERE rc.type = 'conduct' AND rc.ref_id = '25' AND c.locked = 'N' AND rc.private != 'Y' AND seen = 'false';
运行于＆lt; ，5S
+----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
| 1 | SIMPLE | c | ALL | PRIMARY | NULL | NULL | NULL | 3797 | Using where |
| 1 | SIMPLE | rc | ref | recent_changes_user_id_idx,idx_recent_changes_user_case,idx_recent_changes_case | idx_recent_changes_case | 5 | hsaedmp_jason.c.id | 20 | Using where |
| 1 | SIMPLE | u | eq_ref | PRIMARY | PRIMARY | 4 | hsaedmp_jason.rc.user_id | 1 | Using index |
+----+-------------+-------+--------+---------------------------------------------------------------------------------+-------------------------+---------+--------------------------+------+-------------+
在＆gt;中运行4S
caseKey = NULL，这不好。
recent_changes我很困惑，EXPLAIN显示ref_id表没有使用密钥，但似乎+----+-------------+-------+------------+--------+----------------------------------------------------------------------------------------------------------------------------------
---+------------------------+---------+--------------------------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys
| key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+--------+----------------------------------------------------------------------------------------------------------------------------------
---+------------------------+---------+--------------------------+------+----------+-------------+
| 1 | SIMPLE | rc | NULL | ref | recent_changes_user_id_idx,idx_recent_changes_user_case,idx_recent_changes_case,idx_recent_changes_case_date,idx_recent_changes_r
ef | idx_recent_changes_ref | 5 | const | 2096 | 3.12 | Using where |
| 1 | SIMPLE | u | NULL | eq_ref | PRIMARY
| PRIMARY | 4 | hsaedmp_jason.rc.user_id | 1 | 100.00 | Using index |
| 1 | SIMPLE | c | NULL | eq_ref | PRIMARY
| PRIMARY | 4 | hsaedmp_jason.rc.case_id | 1 | 50.00 | Using where |
+----+-------------+-------+------------+--------+----------------------------------------------------------------------------------------------------------------------------------
---+------------------------+---------+--------------------------+------+----------+-------------+
表是需要在recent_changes表上的表{ {1}}栏？
以下是该指数的解释，这里看起来好多了，但我还没能在生产中测试它。
select count(*) as num
FROM (
(
SELECT rc1.*
FROM `user` u1
LEFT JOIN `recent_changes` rc1 on u1.id = rc1.user_id
LEFT JOIN `case` c1 on c1.id = rc1.case_id
WHERE
(rc1.user_id != c1.user_id AND c1.user_id = '1')
AND c1.locked = 'Y'
AND rc1.private != 'Y'
AND seen = 'false'
ORDER BY rc1.datecreated DESC
)
UNION
(
SELECT rc.*
FROM `user` u
LEFT JOIN `recent_changes` rc on u.id = rc.user_id
LEFT JOIN `case` c on c.id = rc.case_id
WHERE
(rc.type = 'conduct' AND rc.ref_id = '1')
AND c.locked = 'Y'
AND rc.private != 'Y'
AND seen = 'false'
ORDER BY rc.datecreated DESC
)
) x;
更新
我使用UNION语句重新编写了查询，更改了JOIN顺序，并在ALTER TABLE recent_changes ADD INDEX idx_recent_changes_notification (type, ref_id, private, seen, user_id);
表上添加了复合索引，使查询响应时间达到＆lt; 10ms。
以下是使用UNION语句的新查询。
d我根据我需要的最终查询创建了索引。
game_deck感谢大家的投入！
答案 0 :(得分：0)
较小的表应放在join子句的第一个。 这取决于表中的记录数。我认为你的用户表是最小的用户表。所以把它放在第一位。似乎'rc'表是最大的一个。你应该把它放在加入的最后。
这是一个例子。
SELECT count(*) as cnt
FROM `user` u
LEFT JOIN `case` c on c.id = rc.case_id
LEFT JOIN `recent_changes` on u.id = rc.user_id
WHERE
(
rc.user_id != c.user_id AND c.user_id = '25'
OR
(rc.type = 'conduct' AND rc.ref_id = '25')
)
AND c.locked = 'N' AND rc.private != 'Y'
AND seen = 'false'
ORDER BY rc.datecreated DESC;
另外，请参阅下面的帖子。这是mssql的事情，但几乎所有的DBMS都有相同的观点
https://www.mssqltips.com/sqlservertutorial/3201/how-join-order-can-affect-the-query-plan/
<强>更新
我审核了你的问题，发现了另一个嫌疑人，这是关于order by子句。 从查询返回的行数很多，“order by”的时间成本会急剧增加。这是我经验中经常遇到的问题。您是否尝试删除order by子句？它快得多吗？