考虑以下模式,第3个表是提到的年/月助手表.辅助表非常常见,可以自然地在整个代码中重复使用.我会留给你加载大量的日期数据.但是请注意每个月的结束日期是为那些想要做更少工作的人组合在一起的,同时允许数据库引擎为我们计算闰年.

您可以在该帮助程序表中只有一列.但是这需要在一些函数中使用函数调用结束日期,这意味着更慢.我们喜欢快.

架构

create table workerRecords

( id int auto_increment primary key,

the_date date not null,

staff_no int not null

);

-- truncate workerRecords;

insert workerRecords(the_date,staff_no) values

('2016-06-10',1),

('2016-06-09',1),

('2016-05-09',1),

('2016-04-09',1),

('2016-03-02',2),

('2016-07-02',2);

create table workers

( staff_no int primary key,

full_name varchar(100) not null

);

-- truncate workers;

insert workers(staff_no,full_name) values

(1,'David Higgins'),(2,"Sally O'Riordan");

下面的助手表

create table ymHelper

( -- Year Month helper table. Used for left joins to pick up all dates.

-- PK is programmer's choice.

dtBegin date primary key, -- by definition not null

dtEnd date null

);

-- truncate ymHelper;

insert ymHelper (dtBegin,dtEnd) values

('2015-01-01',null),('2015-02-01',null),('2015-03-01',null),('2015-04-01',null),('2015-05-01',null),('2015-06-01',null),('2015-07-01',null),('2015-08-01',null),('2015-09-01',null),('2015-10-01',null),('2015-11-01',null),('2015-12-01',null),

('2016-01-01',null),('2016-02-01',null),('2016-03-01',null),('2016-04-01',null),('2016-05-01',null),('2016-06-01',null),('2016-07-01',null),('2016-08-01',null),('2016-09-01',null),('2016-10-01',null),('2016-11-01',null),('2016-12-01',null),

('2017-01-01',null),('2017-02-01',null),('2017-03-01',null),('2017-04-01',null),('2017-05-01',null),('2017-06-01',null),('2017-07-01',null),('2017-08-01',null),('2017-09-01',null),('2017-10-01',null),('2017-11-01',null),('2017-12-01',null),

('2018-01-01',null),('2018-02-01',null),('2018-03-01',null),('2018-04-01',null),('2018-05-01',null),('2018-06-01',null),('2018-07-01',null),('2018-08-01',null),('2018-09-01',null),('2018-10-01',null),('2018-11-01',null),('2018-12-01',null),

('2019-01-01',null),('2019-02-01',null),('2019-03-01',null),('2019-04-01',null),('2019-05-01',null),('2019-06-01',null),('2019-07-01',null),('2019-08-01',null),('2019-09-01',null),('2019-10-01',null),('2019-11-01',null),('2019-12-01',null);

-- will leave as an exercise for you to add more years. Good idea to start, 10 in either direction, at least.

update ymHelper set dtEnd=LAST_DAY(dtBegin); -- data patch. Confirmed leap years.

alter table ymHelper modify dtEnd date not null; -- there, ugly patch above worked fine. Can forget it ever happened (until you add rows)

-- show create table ymHelper; -- this confirms that dtEnd is not null

这是一个帮手表.设置一次并忘记它几年

注意：不要忘记运行上面的更新stmt

快速测试您的查询

SELECT DATE_FORMAT(ymH.dtBegin,'%b %Y') as month,

ifnull(COUNT(wr.the_date),0) as total_records,@soloName as full_name

FROM ymHelper ymH

left join workerRecords wr

on wr.the_date between ymH.dtBegin and ymH.dtEnd

and wr.staff_no = 1 and wr.the_date between '2016-04-01' and '2016-07-31'

LEFT JOIN workers w on w.staff_no = wr.staff_no

cross join (select @soloName:=full_name from workers where staff_no=1) xDerived

WHERE ymH.dtBegin between '2016-04-01' and '2016-07-31'

GROUP BY ymH.dtBegin

order by ymH.dtBegin;

+----------+---------------+---------------+

| month | total_records | full_name |

+----------+---------------+---------------+

| Apr 2016 | 1 | David Higgins |

| May 2016 | 1 | David Higgins |

| Jun 2016 | 2 | David Higgins |

| Jul 2016 | 0 | David Higgins |

+----------+---------------+---------------+

它工作正常.第一个mysql表是Helper表.左连接以引入工作记录(允许为空).我们暂停一下这就是你的问题的重点：缺少数据.最后是一个交叉连接的工作表.

交叉连接是初始化作为工作者名称的变量(@soloName).虽然你请求的缺失日期的空状态通过返回0的ifnull()函数被很好地获取,但是对于工人的名字我们没有那么奢侈.这迫使交叉连接.

交叉连接是笛卡尔积.但由于它是一行,我们不会遇到笛卡尔因导致结果集中许多行的正常问题.无论如何,它的工作原理.

但是这里有一个问题：可以看出,在6个地方维护和插入值太难了.因此,请考虑下面的存储过程.

存储过程

drop procedure if exists getOneWorkersRecCount;

DELIMITER $$

create procedure getOneWorkersRecCount

(pStaffNo int, pBeginDt date, pEndDt date)

BEGIN

SELECT DATE_FORMAT(ymH.dtBegin,'%b %Y') as month,ifnull(COUNT(wr.the_date),0) as total_records,@soloName as full_name

FROM ymHelper ymH

left join workerRecords wr

on wr.the_date between ymH.dtBegin and ymH.dtEnd

and wr.staff_no = pStaffNo and wr.the_date between pBeginDt and pEndDt

LEFT JOIN workers w on w.staff_no = wr.staff_no

cross join (select @soloName:=full_name from workers where staff_no=pStaffNo) xDerived

WHERE ymH.dtBegin between pBeginDt and pEndDt

GROUP BY ymH.dtBegin

order by ymH.dtBegin;

END$$

DELIMITER ;

多次测试存储过程

call getOneWorkersRecCount(1,'2016-04-01','2016-06-09');

call getOneWorkersRecCount(1,'2016-04-01','2016-06-10');

call getOneWorkersRecCount(1,'2016-04-01','2016-07-01');

call getOneWorkersRecCount(2,'2016-02-01','2016-11-01');

啊,更容易使用(在PHP,c#,Java,你的名字).选择是你的,存储过程与否.

奖金存储过程

drop procedure if exists getAllWorkersRecCount;

DELIMITER $$

create procedure getAllWorkersRecCount

(pBeginDt date, pEndDt date)

BEGIN

SELECT DATE_FORMAT(ymH.dtBegin,'%b %Y') as month,ifnull(COUNT(wr.the_date),0) as total_records,w.staff_no,w.full_name

FROM ymHelper ymH

cross join workers w

left join workerRecords wr

on wr.the_date between ymH.dtBegin and ymH.dtEnd

and wr.staff_no = w.staff_no and wr.the_date between pBeginDt and pEndDt

-- LEFT JOIN workers w on w.staff_no = wr.staff_no

-- cross join (select @soloName:=full_name from workers ) xDerived

WHERE ymH.dtBegin between pBeginDt and pEndDt

GROUP BY ymH.dtBegin,w.staff_no,w.full_name

order by ymH.dtBegin,w.staff_no;

END$$

DELIMITER ;

快速测试一下

call getAllWorkersRecCount('2016-03-01','2016-08-01');

+----------+---------------+----------+-----------------+

| month | total_records | staff_no | full_name |

+----------+---------------+----------+-----------------+

| Mar 2016 | 0 | 1 | David Higgins |

| Mar 2016 | 1 | 2 | Sally O'Riordan |

| Apr 2016 | 1 | 1 | David Higgins |

| Apr 2016 | 0 | 2 | Sally O'Riordan |

| May 2016 | 1 | 1 | David Higgins |

| May 2016 | 0 | 2 | Sally O'Riordan |

| Jun 2016 | 2 | 1 | David Higgins |

| Jun 2016 | 0 | 2 | Sally O'Riordan |

| Jul 2016 | 0 | 1 | David Higgins |

| Jul 2016 | 1 | 2 | Sally O'Riordan |

| Aug 2016 | 0 | 1 | David Higgins |

| Aug 2016 | 0 | 2 | Sally O'Riordan |

+----------+---------------+----------+-----------------+

外卖

辅助表已经使用了几十年.不要害怕或不好意思使用它们.事实上,试图在没有它们的情况下完成一些专业工作有时几乎是不可能的.