为什么mysql在使用视图时不使用相同的索引,就像在运行查询whitout视图时一样:
在我发表观点之前我的查询:
DESCRIBE SELECT membership_id, group_id, groups.name AS group_name, citizen_id, citizens.name, citizens.family, citizens.identification, memberships.birth, memberships.death, COALESCE(memberships.death, '2099-12-31 23:59:59') AS to_date
FROM memberships
LEFT JOIN groups ON (group_id = target_id)
LEFT JOIN citizens ON (citizen_id = member_id)
WHERE target_type = 31 AND member_type = 11
AND member_id = 5613956;
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| 1 | SIMPLE | memberships | ref | member,target | member | 10 | const,const | 6 | Using where; Using index |
| 1 | SIMPLE | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
| 1 | SIMPLE | citizens | const | citizen_id | citizen_id | 8 | const | 1 | |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
它可以工作,而且速度很快,每次我想调试成员时,它的编写时间都会有点长。所以我根据该查询创建了一个视图:
CREATE VIEW group_members AS
SELECT membership_id, group_id, groups.name AS group_name, citizen_id, citizens.name, citizens.family, citizens.identification, memberships.birth, memberships.death, COALESCE(memberships.death, '2099-12-31 23:59:59') AS to_date
FROM memberships
LEFT JOIN groups ON (group_id = target_id)
LEFT JOIN citizens ON (citizen_id = member_id)
WHERE target_type = 31 AND member_type = 11;
但是当我尝试获取 5613956 的会员资格时,我得到了这个:
DESCRIBE SELECT * FROM group_members WHERE citizen_id = 5613956;
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
| 1 | SIMPLE | memberships | ref | member,target | target | 1 | const | 5269 | Using where; Using index |
| 1 | SIMPLE | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
| 1 | SIMPLE | citizens | ALL | NULL | NULL | NULL | NULL | 4766712 | Using where |
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
为什么公民的“possible_keys”为NULL?
字段citizen_id 是SERIAL (= BIGINT(20) UNSIGNED UNIQUE NOT NULL AUTO_INCREMENT)
编辑 1
如果我在第一个查询中使用 member_id 的citizen_id,我得到:
DESCRIBE SELECT membership_id, group_id, groups.name AS group_name, citizen_id, citizens.name, citizens.family, citizens.identification, memberships.birth, memberships.death, COALESCE(memberships.death, '2099-12-31 23:59:59') AS to_date
FROM memberships
LEFT JOIN groups ON (group_id = target_id)
LEFT JOIN citizens ON (citizen_id = member_id)
WHERE target_type = 31 AND member_type = 11
AND citizen_id = 5613956;
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| 1 | SIMPLE | citizens | const | citizen_id | citizen_id | 8 | const | 1 | |
| 1 | SIMPLE | memberships | ref | member,target | member | 10 | const,const | 6 | Using where; Using index |
| 1 | SIMPLE | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
编辑 2
ARIGHT JOIN
将问题移至成员表 insted。(1054 x 需要的行,而之前的 4 766 712 x 需要的行)
CREATE VIEW group_members AS
SELECT membership_id, group_id, groups.name AS group_name, citizen_id, citizens.name, citizens.family, citizens.identification, memberships.birth, memberships.death, COALESCE(memberships.death, '2099-12-31 23:59:59') AS to_date
FROM memberships
RIGHT JOIN groups ON (group_id = target_id)
RIGHT JOIN citizens ON (citizen_id = member_id)
WHERE target_type = 31 AND member_type = 11;
DESCRIBE SELECT * FROM group_members WHERE citizen_id = 5613956;
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+-------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+-------+--------------------------+
| 1 | SIMPLE | citizens | const | citizen_id | citizen_id | 8 | const | 1 | |
| 1 | SIMPLE | memberships | index | NULL | member | 45 | NULL | 10540 | Using where; Using index |
| 1 | SIMPLE | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+-------+--------------------------+
编辑 3 一个有趣的注释:这更快,因为它使用索引,视图本身失败
SELECT * FROM (SELECT * FROM group_members) AS t WHERE citizen_id = 5613956;
6 rows in set (0.03 sec)
DESCRIBE SELECT * FROM (SELECT * FROM group_members) AS t WHERE citizen_id = 5613956;
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 4423 | Using where |
| 2 | DERIVED | memberships | ref | member,target | target | 1 | | 5270 | Using where; Using index |
| 2 | DERIVED | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
| 2 | DERIVED | citizens | eq_ref | citizen_id | citizen_id | 8 | interfaceways.memberships.member_id | 1 | |
+----+-------------+-------------+--------+---------------+------------+---------+-------------------------------------+------+--------------------------+
编辑 4 YaKs 评论
CREATE VIEW group_members AS
SELECT membership_id, group_id, groups.name AS group_name, citizen_id, citizens.name, citizens.family, citizens.identification, memberships.birth, memberships.death
FROM memberships
LEFT JOIN groups ON (group_id = target_id)
LEFT JOIN citizens ON (citizen_id = member_id)
WHERE target_type = 31 AND member_type = 11;
DESCRIBE SELECT * FROM group_members WHERE citizen_id = 5613956;
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
| 1 | SIMPLE | memberships | ref | member,target | target | 1 | const | 5270 | Using where; Using index |
| 1 | SIMPLE | groups | eq_ref | group_id | group_id | 8 | interfaceways.memberships.target_id | 1 | |
| 1 | SIMPLE | citizens | ALL | NULL | NULL | NULL | NULL | 4766736 | Using where |
+----+-------------+-------------+--------+---------------+----------+---------+-------------------------------------+---------+--------------------------+
编辑 5 jcho360 评论
ANALYZE TABLE group_members;
+-----------------------------+---------+----------+-------------------------------------------------+
| Table | Op | Msg_type | Msg_text |
+-----------------------------+---------+----------+-------------------------------------------------+
| interfaceways.group_members | analyze | Error | 'interfaceways.group_members' is not BASE TABLE |
| interfaceways.group_members | analyze | error | Corrupt |
+-----------------------------+---------+----------+-------------------------------------------------+
2 rows in set (0.00 sec)
ANALYZE TABLE memberships;
+---------------------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+---------------------------+---------+----------+----------+
| interfaceways.memberships | analyze | status | OK |
+---------------------------+---------+----------+----------+
1 row in set (0.02 sec)
ANALYZE TABLE citizens;
+------------------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+------------------------+---------+----------+----------+
| interfaceways.citizens | analyze | status | OK |
+------------------------+---------+----------+----------+
1 row in set (0.11 sec)
ANALYZE TABLE groups;
+----------------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+----------------------+---------+----------+----------+
| interfaceways.groups | analyze | status | OK |
+----------------------+---------+----------+----------+
1 row in set (0.01 sec)