MySQL hui pūʻulu ma ka hoʻohana? ʻO ka wehewehe kikoʻī o ka hui ma ka helu ʻana i ka waihona MySQL

MySQL E hōʻuluʻulu i ka hui ma ka hoʻohana ʻana?MySQL waihonaʻO ka wehewehe kikoʻī o ka hui ma ka helu

MySQL GROUP BY ʻōlelo

Hoʻonohonoho ka ʻōlelo GROUP BY i ka hopena i hoʻonohonoho ʻia ma luna o hoʻokahi kolamu a ʻoi aku paha.

Ma ke kolamu hui, hiki iā mākou ke hoʻohana i nā hana COUNT, SUM, AVG, etc.

HUI MA ka syntax

SELECT column_name, function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

Hōʻike laʻana

Ke hoʻohana nei ka laʻana ma kēia mokuna i ke ʻano o ka papaʻaina a me ka ʻikepili ma mua o ka hoʻohana ʻana, hiki iā mākou ke hoʻokomo i kēia ʻikepili i loko o ka waihona.

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
--  Table structure for `employee_tbl`
-- ----------------------------
DROP TABLE IF EXISTS `employee_tbl`;
CREATE TABLE `employee_tbl` (
  `id` int(11) NOT NULL,
  `name` char(10) NOT NULL DEFAULT '',
  `date` datetime NOT NULL,
  `singin` tinyint(4) NOT NULL DEFAULT '0' COMMENT '登录次数',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
--  Records of `employee_tbl`
-- ----------------------------
BEGIN;
INSERT INTO `employee_tbl` VALUES ('1', '小明', '2016-04-22 15:25:33', '1'), ('2', '小王', '2016-04-20 15:25:47', '3'), ('3', '小丽', '2016-04-19 15:26:02', '2'), ('4', '小王', '2016-04-07 15:26:14', '4'), ('5', '小明', '2016-04-11 15:26:40', '4'), ('6', '小明', '2016-04-04 15:26:54', '2');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

Ma hope o ka holomua o ka lawe ʻana mai, e hoʻokō i kēia ʻōlelo SQL:

mysql> set names utf8;
mysql> SELECT * FROM employee_tbl;
+----+--------+---------------------+--------+
| id | name   | date                | singin |
+----+--------+---------------------+--------+
|  1 | 小明 | 2016-04-22 15:25:33 |      1 |
|  2 | 小王 | 2016-04-20 15:25:47 |      3 |
|  3 | 小丽 | 2016-04-19 15:26:02 |      2 |
|  4 | 小王 | 2016-04-07 15:26:14 |      4 |
|  5 | 小明 | 2016-04-11 15:26:40 |      4 |
|  6 | 小明 | 2016-04-04 15:26:54 |      2 |
+----+--------+---------------------+--------+
6 rows in set (0.00 sec)

A laila hoʻohana mākou i ka ʻōlelo GROUP BY e hui i ka papa ʻikepili ma ka inoa a helu i ka nui o nā moʻolelo i loaʻa i kēlā me kēia kanaka:

mysql> SELECT name, COUNT(*) FROM   employee_tbl GROUP BY name;
+--------+----------+
| name   | COUNT(*) |
+--------+----------+
| 小丽 |        1 |
| 小明 |        3 |
| 小王 |        2 |
+--------+----------+
3 rows in set (0.01 sec)

E hoʻohana ME ROLLUP

Hiki iā WITH ROLLUP ke hoʻokō i nā helu helu like (SUM, AVG, COUNT...) ma ke kumu o nā helu helu hui.

No ka laʻana, hui mākou i ka papa ʻikepili ma luna ma ka inoa, a laila helu i ka helu o nā manawa i komo ai kēlā me kēia kanaka:

mysql> SELECT name, SUM(singin) as singin_count FROM  employee_tbl GROUP BY name WITH ROLLUP;
+--------+--------------+
| name   | singin_count |
+--------+--------------+
| 小丽 |            2 |
| 小明 |            7 |
| 小王 |            7 |
| NULL   |           16 |
+--------+--------------+
4 rows in set (0.00 sec)

Hōʻike ka moʻolelo NULL i ka helu o nā loina no kēlā me kēia.

Hiki iā mākou ke hoʻohana i ka coalesce e hoʻonoho i kahi inoa hiki ke pani i ka NUll, coalesce syntax:

select coalesce(a,b,c);

ʻO ka wehewehe ʻana: inā a==null, koho b; inā b==null, koho c; inā a!=null, koho i a; inā ʻaʻohe abc, e hoʻihoʻi i ka null (mea ʻole).

Ma kēia hiʻohiʻona inā nele ka inoa, hoʻohana mākou i ka huina:

mysql> SELECT coalesce(name, '总数'), SUM(singin) as singin_count FROM  employee_tbl GROUP BY name WITH ROLLUP;
+--------------------------+--------------+
| coalesce(name, '总数') | singin_count |
+--------------------------+--------------+
| 小丽                   |            2 |
| 小明                   |            7 |
| 小王                   |            7 |
| 总数                   |           16 |
+--------------------------+--------------+
4 rows in set (0.01 sec)