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Mysql 编程实战二
- 创建表
dim_shop
CREATE TABLE dim_shop (
shop_key bigint(20) NOT NULL AUTO_INCREMENT COMMENT 's_poi.id',
shop_id int(11) NOT NULL,
value_date datetime DEFAULT '9999-12-31 00:00:00' COMMENT ' gmt_create from stagedb',
PRIMARY KEY (shop_key),
UNIQUE KEY uidx_dim_shop_id (shop_id,value_date),
UNIQUE KEY uidx_dim_shop_no (value_date)
) ENGINE=InnoDB AUTO_INCREMENT=409557 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
- 往表中插入数据
INSERT INTO mydatabase.dim_shop (shop_key, shop_id, value_date)
VALUES ('41735', '297', '2017-05-26 12:17:21'),
('279978', '297', '2018-03-07 10:10:03'),
('378768', '297', '2018-08-31 13:34:14');
- 测试
join
语句
- 测试1
select
pre.shop_id as shop_id,
pre.value_date as start_date,
cur.value_date as end_date
from mydatabase.dim_shop pre
join mydatabase.dim_shop cur
on cur.shop_id = pre.shop_id;
+---------+---------------------+---------------------+
| shop_id | start_date | end_date |
+---------+---------------------+---------------------+
| 297 | 2017-05-26 12:17:21 | 2017-05-26 12:17:21 |
| 297 | 2017-05-26 12:17:21 | 2018-03-07 10:10:03 |
| 297 | 2017-05-26 12:17:21 | 2018-08-31 13:34:14 |
| 297 | 2018-03-07 10:10:03 | 2017-05-26 12:17:21 |
| 297 | 2018-03-07 10:10:03 | 2018-03-07 10:10:03 |
| 297 | 2018-03-07 10:10:03 | 2018-08-31 13:34:14 |
| 297 | 2018-08-31 13:34:14 | 2017-05-26 12:17:21 |
| 297 | 2018-08-31 13:34:14 | 2018-03-07 10:10:03 |
| 297 | 2018-08-31 13:34:14 | 2018-08-31 13:34:14 |
+---------+---------------------+---------------------+
9 rows in set (0.00 sec)
这么看,就得到了9个结果集。【3*3】
- 测试2
select
pre.shop_id AS shop_id,
pre.value_date AS start_date,
max(cur.value_date) AS end_date
from (mydatabase.dim_shop pre
join mydatabase.dim_shop cur
on((cur.shop_id = pre.shop_id))
);
+---------+---------------------+---------------------+
| shop_id | start_date | end_date |
+---------+---------------------+---------------------+
| 297 | 2017-05-26 12:17:21 | 2018-08-31 13:34:14 |
+---------+---------------------+---------------------+
1 row in set (0.00 sec)
这里的join结果只有1条,是因为是用的是max(cur.value_date) as end_date。所以结果只有1条。
- 测试3
select
pre.shop_id AS shop_id,
pre.value_date AS start_date,
min(cur.value_date) AS end_date
from mydatabase.dim_shop pre
join mydatabase.dim_shop cur
on((cur.shop_id = pre.shop_id))
where (pre.value_date < cur.value_date)
group by pre.shop_id,pre.value_date ;
下面这个SQL语句与上面是等效的:
select
pre.shop_id AS shop_id,
pre.value_date AS start_date,
min(cur.value_date) AS end_date
from mydatabase.dim_shop pre
join mydatabase.dim_shop cur
on((cur.shop_id = pre.shop_id))
where (pre.value_date < cur.value_date)
group by pre.shop_id,pre.value_date;
执行结果
+---------+---------------------+---------------------+
| shop_id | start_date | end_date |
+---------+---------------------+---------------------+
| 297 | 2017-05-26 12:17:21 | 2018-03-07 10:10:03 |
| 297 | 2018-03-07 10:10:03 | 2018-08-31 13:34:14 |
+---------+---------------------+---------------------+
2 rows in set (0.00 sec)