SQL开发知识：mysql 生成连续日期及变量
1、生产连续日期
说明：主要作用于一些统计数据，来根据时间顺序进行显示；
假如数据库数据有隔天数据，偏偏统计又需要每天的都显示，即便是0，那就要生成一个时间表，来使用；
查询数据库数据：
SELECT
DATE_FORMAT( create_time, ‘%Y-%m-%d’ ) AS date,
COUNT(1) AS numb
FROM
qc_task
WHERE
create_time>= DATE_SUB(CURDATE(),INTERVAL 1 MONTH) and
department_id IN ( SELECT id FROM `vigilante_jinan`.`qc_department` WHERE `area_code` = (@dep_BH) AND `status` = ‘1’ AND dept_level >= (@dep_DJ))
GROUP BY DATE_FORMAT( create_time, ‘%Y-%m-%d’ )
DATE_FORMAT( create_time, ‘%Y-%m-%d’ ) AS date,
COUNT(1) AS numb
FROM
qc_task
WHERE
create_time>= DATE_SUB(CURDATE(),INTERVAL 1 MONTH) and
department_id IN ( SELECT id FROM `vigilante_jinan`.`qc_department` WHERE `area_code` = (@dep_BH) AND `status` = ‘1’ AND dept_level >= (@dep_DJ))
GROUP BY DATE_FORMAT( create_time, ‘%Y-%m-%d’ )
隔天时出数据：
这样是不是就不好看了，如果非要说加个order by 1 desc 排一下，也可以…
但是就算排出来，时间也是不连贯的；
生成最近7天的日期：
// 方法笨，但还是有效的
select DATE_FORMAT(SUBDATE(NOW(), interval (timeList.sj*1460) MINUTE),’%Y-%m-%d’) as ‘datetime’ from
(SELECT @num:=@num+1 as sj from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t,
— (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t1, — 假如嫌弃生成的少，打来这个就行
(SELECT @num:=0) y) as timeList
select DATE_FORMAT(SUBDATE(NOW(), interval (timeList.sj*1460) MINUTE),’%Y-%m-%d’) as ‘datetime’ from
(SELECT @num:=@num+1 as sj from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t,
— (SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t1, — 假如嫌弃生成的少，打来这个就行
(SELECT @num:=0) y) as timeList
生成的时间：
生成后使用：
— 生成后左右链接即可，但主表要为时间表
SELECT f.datetime, t.numb FROM
(SELECT
DATE_FORMAT( create_time, ‘%Y-%m-%d’ ) AS date,
COUNT(1) AS numb
FROM
qc_task
WHERE
create_time>= DATE_SUB(CURDATE(),INTERVAL 1 MONTH) and
department_id IN ( SELECT id FROM `vigilante_jinan`.`qc_department` WHERE `area_code` = (@dep_BH) AND `status` = ‘1’ AND dept_level >= (@dep_DJ))
GROUP BY DATE_FORMAT( create_time, ‘%Y-%m-%d’ )) t
right join
(select DATE_FORMAT(SUBDATE(NOW(), interval (timeList.sj*1460) MINUTE),’%Y-%m-%d’) as ‘datetime’ from
(SELECT @num:=@num+1 as sj from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t,
(SELECT @num:=0) y) as timeList) f on t.date = f.datetime ;
SELECT f.datetime, t.numb FROM
(SELECT
DATE_FORMAT( create_time, ‘%Y-%m-%d’ ) AS date,
COUNT(1) AS numb
FROM
qc_task
WHERE
create_time>= DATE_SUB(CURDATE(),INTERVAL 1 MONTH) and
department_id IN ( SELECT id FROM `vigilante_jinan`.`qc_department` WHERE `area_code` = (@dep_BH) AND `status` = ‘1’ AND dept_level >= (@dep_DJ))
GROUP BY DATE_FORMAT( create_time, ‘%Y-%m-%d’ )) t
right join
(select DATE_FORMAT(SUBDATE(NOW(), interval (timeList.sj*1460) MINUTE),’%Y-%m-%d’) as ‘datetime’ from
(SELECT @num:=@num+1 as sj from
(SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7) t,
(SELECT @num:=0) y) as timeList) f on t.date = f.datetime ;
使用后效果：
我这里是数据库没有数据…所以看不到有数量显示
2、变量赋值
看到第一个里面 @符号很多是吗，那些都是变量，如果把查询语句放进去，整个查询语句就显得太臃肿了，会很长…所以有些东西可以拆分出去；
比如在查询数据库语句中的：
来看下他们的真面目：
# 查询部门区域编号
SELECT @dep_BH:=(SELECT area_code FROM qc_department WHERE dept_name = “历下区”);
# 查询部门等级
SELECT @dep_DJ:=(SELECT dept_level FROM qc_department WHERE dept_name = “历下区”);
SELECT @dep_BH:=(SELECT area_code FROM qc_department WHERE dept_name = “历下区”);
# 查询部门等级
SELECT @dep_DJ:=(SELECT dept_level FROM qc_department WHERE dept_name = “历下区”);
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