在网站上实施了一项新功能，就好像它是一个“社交网络”。
用户制作，接收消息和内容的各种操作。他们的朋友可以看到所有动作。
class userMuralEntry(models.Model):
user_src = models.ForeignKey(userInfo, related_name="user_src")
user = models.ManyToManyField(userInfo, related_name="user_dest")
user_follow = models.ManyToManyField(userInfo, related_name="user_follow")
private = models.BooleanField(default=False)
content = models.TextField()
date = models.DateTimeField(default=datetime.now)
last_update = models.DateTimeField()
object_type = models.ForeignKey(muralType)
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey('content_type', 'object_id')
每当我访问我的首页时，我都会收到所有朋友的动作，除了私人动作。 所以，我做了这个django模型查询
mural_list = db.userMuralEntry.objects.filter(Q(user__pk__in=friend_list)|Q(user_src__pk__in=friend_list)).order_by('-last_update')
m = mural_list.exclude(
Q(private=True),
~Q(user_src=me_db) & ~Q(user=me_db))
m = m.distinct()
所有这些代码都会生成这个BIG查询（这里有解释输出）
SELECT DISTINCT myps3t_usermuralentry.id,
myps3t_usermuralentry.user_src_id,
myps3t_usermuralentry.private,
myps3t_usermuralentry.content,
myps3t_usermuralentry.DATE,
myps3t_usermuralentry.last_update,
myps3t_usermuralentry.object_type_id,
myps3t_usermuralentry.content_type_id,
myps3t_usermuralentry.object_id
FROM myps3t_usermuralentry
LEFT OUTER JOIN myps3t_usermuralentry_user
ON ( myps3t_usermuralentry.id =
myps3t_usermuralentry_user.usermuralentry_id )
LEFT OUTER JOIN myps3t_userinfo t4
ON ( myps3t_usermuralentry.user_src_id = t4.id )
WHERE ( ( myps3t_usermuralentry_user.userinfo_id = 20877
OR myps3t_usermuralentry.user_src_id = 20877 )
AND NOT ( myps3t_usermuralentry.private = 1
AND ( NOT (( t4.id = 21095
AND NOT ( t4.id IS NULL ) ))
AND NOT ( myps3t_usermuralentry.id IN
(SELECT u1.usermuralentry_id
FROM
myps3t_usermuralentry_user u1
WHERE (
u1.userinfo_id =
21095
AND
u1.usermuralentry_id
IS
NOT
NULL
)) ) ) )
)
ORDER BY myps3t_usermuralentry.last_update;
mysql> explain SELECT DISTINCT `myps3t_usermuralentry`.`id`, `myps3t_usermuralentry`.`user_src_id`, `myps3t_usermuralentry`.`private`, `myps3t_usermuralentry`.`content`, `myps3t_usermuralentry`.`date`, `myps3t_usermuralentry`.`last_update`, `myps3t_usermuralentry`.`object_type_id`, `myps3t_usermuralentry`.`content_type_id`, `myps3t_usermuralentry`.`object_id` FROM `myps3t_usermuralentry` LEFT OUTER JOIN `myps3t_usermuralentry_user` ON (`myps3t_usermuralentry`.`id` = `myps3t_usermuralentry_user`.`usermuralentry_id`) LEFT OUTER JOIN `myps3t_userinfo` T4 ON (`myps3t_usermuralentry`.`user_src_id` = T4.`id`) WHERE ((`myps3t_usermuralentry_user`.`userinfo_id` = 20877 OR `myps3t_usermuralentry`.`user_src_id` = 20877 ) AND NOT (`myps3t_usermuralentry`.`private` = 1 AND (NOT ((T4.`id` = 21095 AND NOT (T4.`id` IS NULL))) AND NOT (`myps3t_usermuralentry`.`id` IN (SELECT U1.`usermuralentry_id` FROM `myps3t_usermuralentry_user` U1 WHERE (U1.`userinfo_id` = 21095 AND U1.`usermuralentry_id` IS NOT NULL)))))) ORDER BY `myps3t_usermuralentry`.`last_update` DESC LIMIT 20;
+----+--------------------+----------------------------+-----------------+-------------------------------------------------------------------------------------------+-------------------+---------+---------------------------------------------------+--------+------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+----------------------------+-----------------+-------------------------------------------------------------------------------------------+-------------------+---------+---------------------------------------------------+--------+------------------------------------+
| 1 | PRIMARY | myps3t_usermuralentry | ALL | myps3t_usermuralentry_99bd10ae | NULL | NULL | NULL | 665410 | Using temporary; Using filesort |
| 1 | PRIMARY | myps3t_usermuralentry_user | ref | usermuralentry_id,myps3t_usermuralentry_user_bcd7114e | usermuralentry_id | 4 | fabriciols_ps3t.myps3t_usermuralentry.id | 2 | Using where; Using index; Distinct |
| 1 | PRIMARY | T4 | eq_ref | PRIMARY | PRIMARY | 4 | fabriciols_ps3t.myps3t_usermuralentry.user_src_id | 1 | Using where; Using index; Distinct |
| 2 | DEPENDENT SUBQUERY | U1 | unique_subquery | usermuralentry_id,myps3t_usermuralentry_user_bcd7114e,myps3t_usermuralentry_user_6b192ca7 | usermuralentry_id | 8 | func,const | 1 | Using index; Using where |
+----+--------------------+----------------------------+-----------------+-------------------------------------------------------------------------------------------+-------------------+---------+---------------------------------------------------+--------+------------------------------------+
4 rows in set (0.00 sec)
mysql> show indexes from myps3t_usermuralentry ;
+-----------------------+------------+--------------------------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------------------+------------+--------------------------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+
| myps3t_usermuralentry | 0 | PRIMARY | 1 | id | A | 665410 | NULL | NULL | | BTREE | |
| myps3t_usermuralentry | 1 | myps3t_usermuralentry_99bd10ae | 1 | user_src_id | A | 22180 | NULL | NULL | | BTREE | |
| myps3t_usermuralentry | 1 | myps3t_usermuralentry_ae71a55b | 1 | object_type_id | A | 8 | NULL | NULL | | BTREE | |
| myps3t_usermuralentry | 1 | myps3t_usermuralentry_e4470c6e | 1 | content_type_id | A | 13 | NULL | NULL | | BTREE | |
+-----------------------+------------+--------------------------------+--------------+-----------------+-----------+-------------+----------+--------+------+------------+---------+
6 rows in set (0.00 sec)
我对索引做了一些调整，但是它太慢了......一个有3-4个朋友的用户就像5秒钟一样！
此表目前有500,000行。
有些改进的想法？我的django代码是否凌乱？最好自己动手查询？
答案 0 :(得分：2)
您需要再次阅读：https://docs.djangoproject.com/en/dev/topics/db/queries/
您可以通过多种方式简化代码。例如：
mural_list = db.userMuralEntry.objects.filter(Q(user__pk__in=friend_list)|Q(user_src__pk__in=friend_list))
相当于：
mural_list = db.userMuralEntry.objects.filter(user__pk__in=friend_list)|db.userMuralEntry.objects.filter(user_src__pk__in=friend_list)
和
m = mural_list.exclude(
Q(private=True),
~Q(user_src=me_db) & ~Q(user=me_db))
相当于
m = mural_list.exclude(private=True).exclude(user_src=me_db).exclude(user=me_db)
请注意，最好在最后放置order_by子句，以避免对ordered_by查询进行外连接。
最终优化的sql由@fabriciols在这里分享：http://chat.stackoverflow.com/transcript/message/2795524#2795524