MySQL sum group e ala ile fa'aoga? Faʻamatalaga auiliili o le vaega e ala ile faitau ile MySQL database

MySQL Fa'aopoopo vaega ile fa'aoga?MySQL databaseFa'amatalaga auiliili ole vaega ile faitau

MySQL GROUP BY faʻamatalaga

O le fa'amatalaga GROUP BY fa'aputu fa'aputuga fa'atatau ile tasi pe sili atu koluma.

I luga o le koluma tu'ufa'atasi e mafai ona tatou fa'aogaina galuega COUNT, SUM, AVG, ma isi.

VAEGA I le syntax

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

Fa'ata'ita'iga fa'ata'ita'iga

O le faʻataʻitaʻiga i lenei mataupu e faʻaogaina ai le faʻatulagaina o laulau ma faʻamaumauga o loʻo i lalo. Aʻo leʻi faʻaaogaina, e mafai ona matou faʻaulufaleina mai faʻamatalaga nei i totonu o le database.

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;

A maeʻa le faʻaulufale mai, faʻatino le faʻamatalaga SQL lea:

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)

Ona sosoo ai lea ma le fa'aogaina o le fa'amatalaga GROUP BY e fa'avasega ai le laulau fa'amaumauga i le igoa ma faitau pe fia fa'amaumauga a tagata ta'ito'atasi:

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)

Fa'aaoga MA ROLLUP

WITH ROLLUP e mafai ona fa'atinoina fa'amaumauga tutusa (SUM, AVG, COUNT...) i luga o fa'avae o fa'amaumauga tu'ufa'atasi.

Mo se faʻataʻitaʻiga, matou te faʻavasegaina le laulau faʻamaumauga o loʻo i luga i le igoa, ona faitau lea o le aofaʻi o taimi e ulufale ai tagata taʻitasi:

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)

O le fa'amaumauga NULL o lo'o fa'atusalia le numera o saini mo tagata uma.

E mafai ona tatou faʻaoga faʻatasi e seti ai se igoa e mafai ona suitulaga i le NUll, coalesce syntax:

select coalesce(a,b,c);

Fa'amatalaga Parameter: afai a==null, filifili le b;afai b==null, filifili c;afai a!=null, filifili a;afai ole abc e null, toe fa'afo'i le null (leai se uiga).

I le faʻataʻitaʻiga o loʻo i lalo pe a leai le igoa matou te faʻaogaina le aofaʻi nai lo:

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)