我有两个表，只说一个用户表和一个日期表。他们看起来像这样：
用户
ID_User | Title | Firstname | Surname | JobNumber
1 | Mr | Bob | Smith | JOB001
2 | Mrs | Bobbi | Smythe | JOB001
...
13000
日期
ID_Date | ID_User | DateType | DateAssigned | JobNumber
1 | 1 | Intent | 21-Jun-2016 | JOB001
2 | 1 | Reg | 21-Apr-2017 | JOB001
3 | 1 | Flight | 21-May-2017 | JOB001
4 | 2 | Intent | 09-Dec-2016 | JOB001
5 | 2 | Flight | 01-Jan-2017 | JOB001
...
5000
唯一索引是ID_User + DateType + JobNumber。
可能有任意数量的DateType。
当我进行如下查询时，需要花费一些时间。
select
ID_User,
Title,
Firstname,
Surname,
JobNumber,
DI.DateAssigned as Date_Intent,
DR.DateAssigned as Date_Reg,
DF.DateAssigned as Date_Flight
from
User as U
left join Dates as DI on U.ID_User = DI.ID_User
and DI.JobNumber = "JOB001"
and DI.DateType = "Intent"
left join Dates as DR on U.ID_User = DR.ID_User
and DR.JobNumber = "JOB001"
and DR.DateType = "Reg"
left join Dates as DF on U.ID_User = DF.ID_User
and DF.JobNumber = "JOB001"
and DF.DateType = "Flight"
where
U.JobNumber = "JOB001"
order by
U.Surname,
U.Firstname;
每个JobNumber只能容纳300个人，最多可以说5种不同的日期类型。
为什么要花这么长时间？我们正在谈论2分钟。
还有另一种写方法吗？
日期表：
CREATE TABLE `ATL_V2_Assigned_Dates` (
`ID_Date` bigint(7) unsigned NOT NULL AUTO_INCREMENT,
`JobNumber` varchar(10) NOT NULL DEFAULT '',
`ID_User` bigint(7) unsigned NOT NULL DEFAULT '0',
`DateAssigned` datetime NOT NULL,
`DateType` varchar(100) NOT NULL,
`Comment` text NOT NULL,
`Updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`Inserted` datetime NOT NULL,
PRIMARY KEY (`ID_Date`),
UNIQUE KEY `ID_Date` (`ID_Date`) USING BTREE,
UNIQUE KEY `unq_idx` (`JobNumber`,`ID_User`,`DateType`) USING BTREE,
KEY `JobNumber` (`JobNumber`) USING BTREE,
KEY `ID_User` (`ID_User`) USING BTREE,
KEY `DateType` (`DateType`) USING BTREE
) ENGINE=MyISAM AUTO_INCREMENT=3975 DEFAULT CHARSET=utf8;
更新2017年1月12日
非常奇怪，查询现在以0.06s的速度运行，以下是输出：
explain select
U.ID_User,
U.Title,
U.Firstname,
U.Surname,
U.JobNumber,
DI.DateAssigned as Date_Intent,
DR.DateAssigned as Date_Reg,
DF.DateAssigned as Date_Flight
from
ATL_Users as U
left join ATL_V2_Assigned_Dates as DI on U.ID_User = DI.ID_User
and DI.JobNumber = "ACI001"
and DI.DateType = "Deadline - Intention"
left join ATL_V2_Assigned_Dates as DR on U.ID_User = DR.ID_User
and DR.JobNumber = "ACI001"
and DR.DateType = "Event - Registration"
left join ATL_V2_Assigned_Dates as DF on U.ID_User = DF.ID_User
and DF.JobNumber = "ACI001"
and DF.DateType = "Deadline - Flight"
where
U.JobNumber = "ACI001"
order by
U.Surname,
U.Firstname;
+----+-------------+-------+--------+------------------------------------+-----------+---------+------------------------------------+------+----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+------------------------------------+-----------+---------+------------------------------------+------+----------------------------------------------------+
| 1 | SIMPLE | U | ref | JobNumber | JobNumber | 32 | const | 506 | Using index condition; Using where; Using filesort |
| 1 | SIMPLE | DI | eq_ref | unq_idx,JobNumber,ID_User,DateType | unq_idx | 342 | const,cclliveo_atl.U.ID_User,const | 1 | Using where |
| 1 | SIMPLE | DR | eq_ref | unq_idx,JobNumber,ID_User,DateType | unq_idx | 342 | const,cclliveo_atl.U.ID_User,const | 1 | Using where |
| 1 | SIMPLE | DF | eq_ref | unq_idx,JobNumber,ID_User,DateType | unq_idx | 342 | const,cclliveo_atl.U.ID_User,const | 1 | Using where |
+----+-------------+-------+--------+------------------------------------+-----------+---------+------------------------------------+------+----------------------------------------------------+
我不知道我/我们做了什么，是否有人可以指出您的答案，然后我将其打勾。谢谢你们。
最佳答案
您可以尝试条件聚合来避免所有这些连接
给定
drop table if exists Userjobs;
create table userjobs (ID_User int, Title varchar(10), Firstname varchar(10), Surname varchar(10), JobNumber varchar(10));
insert into userjobs values
(1 , 'Mr' , 'Bob' , 'Smith' , 'JOB001'),
(2 , 'Mrs' , 'Bobbi', 'Smythe' , 'JOB001');
drop table if exists jobDates;
create table jobdates(ID_Date int, ID_User int, DateType varchar(10), DateAssigned date, JobNumber varchar(10));
insert into jobdates values
(1 , 1 , 'Intent' , '2016-06-21' , 'JOB001'),
(2 , 1 , 'Reg' , '2017-04-21' , 'JOB001'),
(3 , 1 , 'Flight' , '2017-05-21' , 'JOB001'),
(4 , 2 , 'Intent' , '2016-12-09' , 'JOB001'),
(5 , 2 , 'Flight' , '2017-01-01' , 'JOB001');
MariaDB [sandbox]> select
-> u.ID_User,
-> Title,
-> Firstname,
-> Surname,
-> u.JobNumber,
-> max(case when datetype = 'intent' then dateassigned else null end) as intent,
-> max(case when datetype = 'reg' then dateassigned else null end) reg,
-> max(case when datetype = 'flight' then dateassigned else null end) as flight
-> from
-> Userjobs as U
-> left join jobDates as jd on U.ID_User = jd.ID_User
-> and jd.JobNumber = u.jobnumber
-> where u.jobnumber = 'JOB001'
-> group by u.ID_User,
-> Title,
-> Firstname,
-> Surname,
-> u.JobNumber;
+---------+-------+-----------+---------+-----------+------------+------------+------------+
| ID_User | Title | Firstname | Surname | JobNumber | intent | reg | flight |
+---------+-------+-----------+---------+-----------+------------+------------+------------+
| 1 | Mr | Bob | Smith | JOB001 | 2016-06-21 | 2017-04-21 | 2017-05-21 |
| 2 | Mrs | Bobbi | Smythe | JOB001 | 2016-12-09 | NULL | 2017-01-01 |
+---------+-------+-----------+---------+-----------+------------+------------+------------+
2 rows in set (0.00 sec)