《MySQL 基础篇》二：入门

Author: ACatSmiling

Since: 2024-09-18

MySQL 的基本使用

MySQL 语法规范：

  • 不区分大小写；
  • 每句话用;或\g结尾；
  • 各子句一般分行写；
  • 关键字不能缩写，也不能分行；
  • 用缩进提高语句的可读性。

进入容器，并与 MySQL 客户端交互：

# 进入 MySQL 客户端：-u 用户名，-p 密码，-P 端口
$ mysql -uroot -proot -P3306
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 15
Server version: 8.0.29 MySQL Community Server - GPL

Copyright (c) 2000, 2022, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

  • 执行建库脚本：

    /*
SQLyog Ultimate v12.08 (64 bit)
MySQL - 5.7.28-log : Database - atguigudb
*********************************************************************
*/


/*!40101 SET NAMES utf8 */;

/*!40101 SET SQL_MODE=''*/;

/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;
CREATE DATABASE /*!32312 IF NOT EXISTS*/`atguigudb` /*!40100 DEFAULT CHARACTER SET utf8 */;

USE `atguigudb`;

/*Table structure for table `countries` */

DROP TABLE IF EXISTS `countries`;

CREATE TABLE `countries` (
  `country_id` char(2) NOT NULL,
  `country_name` varchar(40) DEFAULT NULL,
  `region_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`country_id`),
  KEY `countr_reg_fk` (`region_id`),
  CONSTRAINT `countr_reg_fk` FOREIGN KEY (`region_id`) REFERENCES `regions` (`region_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `countries` */

insert  into `countries`(`country_id`,`country_name`,`region_id`) values ('AR','Argentina',2),('AU','Australia',3),('BE','Belgium',1),('BR','Brazil',2),('CA','Canada',2),('CH','Switzerland',1),('CN','China',3),('DE','Germany',1),('DK','Denmark',1),('EG','Egypt',4),('FR','France',1),('HK','HongKong',3),('IL','Israel',4),('IN','India',3),('IT','Italy',1),('JP','Japan',3),('KW','Kuwait',4),('MX','Mexico',2),('NG','Nigeria',4),('NL','Netherlands',1),('SG','Singapore',3),('UK','United Kingdom',1),('US','United States of America',2),('ZM','Zambia',4),('ZW','Zimbabwe',4);

/*Table structure for table `departments` */

DROP TABLE IF EXISTS `departments`;

CREATE TABLE `departments` (
  `department_id` int(4) NOT NULL DEFAULT '0',
  `department_name` varchar(30) NOT NULL,
  `manager_id` int(6) DEFAULT NULL,
  `location_id` int(4) DEFAULT NULL,
  PRIMARY KEY (`department_id`),
  UNIQUE KEY `dept_id_pk` (`department_id`),
  KEY `dept_loc_fk` (`location_id`),
  KEY `dept_mgr_fk` (`manager_id`),
  CONSTRAINT `dept_loc_fk` FOREIGN KEY (`location_id`) REFERENCES `locations` (`location_id`),
  CONSTRAINT `dept_mgr_fk` FOREIGN KEY (`manager_id`) REFERENCES `employees` (`employee_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `departments` */

insert  into `departments`(`department_id`,`department_name`,`manager_id`,`location_id`) values (10,'Administration',200,1700),(20,'Marketing',201,1800),(30,'Purchasing',114,1700),(40,'Human Resources',203,2400),(50,'Shipping',121,1500),(60,'IT',103,1400),(70,'Public Relations',204,2700),(80,'Sales',145,2500),(90,'Executive',100,1700),(100,'Finance',108,1700),(110,'Accounting',205,1700),(120,'Treasury',NULL,1700),(130,'Corporate Tax',NULL,1700),(140,'Control And Credit',NULL,1700),(150,'Shareholder Services',NULL,1700),(160,'Benefits',NULL,1700),(170,'Manufacturing',NULL,1700),(180,'Construction',NULL,1700),(190,'Contracting',NULL,1700),(200,'Operations',NULL,1700),(210,'IT Support',NULL,1700),(220,'NOC',NULL,1700),(230,'IT Helpdesk',NULL,1700),(240,'Government Sales',NULL,1700),(250,'Retail Sales',NULL,1700),(260,'Recruiting',NULL,1700),(270,'Payroll',NULL,1700);

/*Table structure for table `employees` */

DROP TABLE IF EXISTS `employees`;

CREATE TABLE `employees` (
  `employee_id` int(6) NOT NULL DEFAULT '0',
  `first_name` varchar(20) DEFAULT NULL,
  `last_name` varchar(25) NOT NULL,
  `email` varchar(25) NOT NULL,
  `phone_number` varchar(20) DEFAULT NULL,
  `hire_date` date NOT NULL,
  `job_id` varchar(10) NOT NULL,
  `salary` double(8,2) DEFAULT NULL,
  `commission_pct` double(2,2) DEFAULT NULL,
  `manager_id` int(6) DEFAULT NULL,
  `department_id` int(4) DEFAULT NULL,
  PRIMARY KEY (`employee_id`),
  UNIQUE KEY `emp_email_uk` (`email`),
  UNIQUE KEY `emp_emp_id_pk` (`employee_id`),
  KEY `emp_dept_fk` (`department_id`),
  KEY `emp_job_fk` (`job_id`),
  KEY `emp_manager_fk` (`manager_id`),
  CONSTRAINT `emp_dept_fk` FOREIGN KEY (`department_id`) REFERENCES `departments` (`department_id`),
  CONSTRAINT `emp_job_fk` FOREIGN KEY (`job_id`) REFERENCES `jobs` (`job_id`),
  CONSTRAINT `emp_manager_fk` FOREIGN KEY (`manager_id`) REFERENCES `employees` (`employee_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `employees` */

insert  into `employees`(`employee_id`,`first_name`,`last_name`,`email`,`phone_number`,`hire_date`,`job_id`,`salary`,`commission_pct`,`manager_id`,`department_id`) values (100,'Steven','King','SKING','515.123.4567','1987-06-17','AD_PRES',24000.00,NULL,NULL,90),(101,'Neena','Kochhar','NKOCHHAR','515.123.4568','1989-09-21','AD_VP',17000.00,NULL,100,90),(102,'Lex','De Haan','LDEHAAN','515.123.4569','1993-01-13','AD_VP',17000.00,NULL,100,90),(103,'Alexander','Hunold','AHUNOLD','590.423.4567','1990-01-03','IT_PROG',9000.00,NULL,102,60),(104,'Bruce','Ernst','BERNST','590.423.4568','1991-05-21','IT_PROG',6000.00,NULL,103,60),(105,'David','Austin','DAUSTIN','590.423.4569','1997-06-25','IT_PROG',4800.00,NULL,103,60),(106,'Valli','Pataballa','VPATABAL','590.423.4560','1998-02-05','IT_PROG',4800.00,NULL,103,60),(107,'Diana','Lorentz','DLORENTZ','590.423.5567','1999-02-07','IT_PROG',4200.00,NULL,103,60),(108,'Nancy','Greenberg','NGREENBE','515.124.4569','1994-08-17','FI_MGR',12000.00,NULL,101,100),(109,'Daniel','Faviet','DFAVIET','515.124.4169','1994-08-16','FI_ACCOUNT',9000.00,NULL,108,100),(110,'John','Chen','JCHEN','515.124.4269','1997-09-28','FI_ACCOUNT',8200.00,NULL,108,100),(111,'Ismael','Sciarra','ISCIARRA','515.124.4369','1997-09-30','FI_ACCOUNT',7700.00,NULL,108,100),(112,'Jose Manuel','Urman','JMURMAN','515.124.4469','1998-03-07','FI_ACCOUNT',7800.00,NULL,108,100),(113,'Luis','Popp','LPOPP','515.124.4567','1999-12-07','FI_ACCOUNT',6900.00,NULL,108,100),(114,'Den','Raphaely','DRAPHEAL','515.127.4561','1994-12-07','PU_MAN',11000.00,NULL,100,30),(115,'Alexander','Khoo','AKHOO','515.127.4562','1995-05-18','PU_CLERK',3100.00,NULL,114,30),(116,'Shelli','Baida','SBAIDA','515.127.4563','1997-12-24','PU_CLERK',2900.00,NULL,114,30),(117,'Sigal','Tobias','STOBIAS','515.127.4564','1997-07-24','PU_CLERK',2800.00,NULL,114,30),(118,'Guy','Himuro','GHIMURO','515.127.4565','1998-11-15','PU_CLERK',2600.00,NULL,114,30),(119,'Karen','Colmenares','KCOLMENA','515.127.4566','1999-08-10','PU_CLERK',2500.00,NULL,114,30),(120,'Matthew','Weiss','MWEISS','650.123.1234','1996-07-18','ST_MAN',8000.00,NULL,100,50),(121,'Adam','Fripp','AFRIPP','650.123.2234','1997-04-10','ST_MAN',8200.00,NULL,100,50),(122,'Payam','Kaufling','PKAUFLIN','650.123.3234','1995-05-01','ST_MAN',7900.00,NULL,100,50),(123,'Shanta','Vollman','SVOLLMAN','650.123.4234','1997-10-10','ST_MAN',6500.00,NULL,100,50),(124,'Kevin','Mourgos','KMOURGOS','650.123.5234','1999-11-16','ST_MAN',5800.00,NULL,100,50),(125,'Julia','Nayer','JNAYER','650.124.1214','1997-07-16','ST_CLERK',3200.00,NULL,120,50),(126,'Irene','Mikkilineni','IMIKKILI','650.124.1224','1998-09-28','ST_CLERK',2700.00,NULL,120,50),(127,'James','Landry','JLANDRY','650.124.1334','1999-01-14','ST_CLERK',2400.00,NULL,120,50),(128,'Steven','Markle','SMARKLE','650.124.1434','2000-03-08','ST_CLERK',2200.00,NULL,120,50),(129,'Laura','Bissot','LBISSOT','650.124.5234','1997-08-20','ST_CLERK',3300.00,NULL,121,50),(130,'Mozhe','Atkinson','MATKINSO','650.124.6234','1997-10-30','ST_CLERK',2800.00,NULL,121,50),(131,'James','Marlow','JAMRLOW','650.124.7234','1997-02-16','ST_CLERK',2500.00,NULL,121,50),(132,'TJ','Olson','TJOLSON','650.124.8234','1999-04-10','ST_CLERK',2100.00,NULL,121,50),(133,'Jason','Mallin','JMALLIN','650.127.1934','1996-06-14','ST_CLERK',3300.00,NULL,122,50),(134,'Michael','Rogers','MROGERS','650.127.1834','1998-08-26','ST_CLERK',2900.00,NULL,122,50),(135,'Ki','Gee','KGEE','650.127.1734','1999-12-12','ST_CLERK',2400.00,NULL,122,50),(136,'Hazel','Philtanker','HPHILTAN','650.127.1634','2000-02-06','ST_CLERK',2200.00,NULL,122,50),(137,'Renske','Ladwig','RLADWIG','650.121.1234','1995-07-14','ST_CLERK',3600.00,NULL,123,50),(138,'Stephen','Stiles','SSTILES','650.121.2034','1997-10-26','ST_CLERK',3200.00,NULL,123,50),(139,'John','Seo','JSEO','650.121.2019','1998-02-12','ST_CLERK',2700.00,NULL,123,50),(140,'Joshua','Patel','JPATEL','650.121.1834','1998-04-06','ST_CLERK',2500.00,NULL,123,50),(141,'Trenna','Rajs','TRAJS','650.121.8009','1995-10-17','ST_CLERK',3500.00,NULL,124,50),(142,'Curtis','Davies','CDAVIES','650.121.2994','1997-01-29','ST_CLERK',3100.00,NULL,124,50),(143,'Randall','Matos','RMATOS','650.121.2874','1998-03-15','ST_CLERK',2600.00,NULL,124,50),(144,'Peter','Vargas','PVARGAS','650.121.2004','1998-07-09','ST_CLERK',2500.00,NULL,124,50),(145,'John','Russell','JRUSSEL','011.44.1344.429268','1996-10-01','SA_MAN',14000.00,0.40,100,80),(146,'Karen','Partners','KPARTNER','011.44.1344.467268','1997-01-05','SA_MAN',13500.00,0.30,100,80),(147,'Alberto','Errazuriz','AERRAZUR','011.44.1344.429278','1997-03-10','SA_MAN',12000.00,0.30,100,80),(148,'Gerald','Cambrault','GCAMBRAU','011.44.1344.619268','1999-10-15','SA_MAN',11000.00,0.30,100,80),(149,'Eleni','Zlotkey','EZLOTKEY','011.44.1344.429018','2000-01-29','SA_MAN',10500.00,0.20,100,80),(150,'Peter','Tucker','PTUCKER','011.44.1344.129268','1997-01-30','SA_REP',10000.00,0.30,145,80),(151,'David','Bernstein','DBERNSTE','011.44.1344.345268','1997-03-24','SA_REP',9500.00,0.25,145,80),(152,'Peter','Hall','PHALL','011.44.1344.478968','1997-08-20','SA_REP',9000.00,0.25,145,80),(153,'Christopher','Olsen','COLSEN','011.44.1344.498718','1998-03-30','SA_REP',8000.00,0.20,145,80),(154,'Nanette','Cambrault','NCAMBRAU','011.44.1344.987668','1998-12-09','SA_REP',7500.00,0.20,145,80),(155,'Oliver','Tuvault','OTUVAULT','011.44.1344.486508','1999-11-23','SA_REP',7000.00,0.15,145,80),(156,'Janette','King','JKING','011.44.1345.429268','1996-01-30','SA_REP',10000.00,0.35,146,80),(157,'Patrick','Sully','PSULLY','011.44.1345.929268','1996-03-04','SA_REP',9500.00,0.35,146,80),(158,'Allan','McEwen','AMCEWEN','011.44.1345.829268','1996-08-01','SA_REP',9000.00,0.35,146,80),(159,'Lindsey','Smith','LSMITH','011.44.1345.729268','1997-03-10','SA_REP',8000.00,0.30,146,80),(160,'Louise','Doran','LDORAN','011.44.1345.629268','1997-12-15','SA_REP',7500.00,0.30,146,80),(161,'Sarath','Sewall','SSEWALL','011.44.1345.529268','1998-11-03','SA_REP',7000.00,0.25,146,80),(162,'Clara','Vishney','CVISHNEY','011.44.1346.129268','1997-11-11','SA_REP',10500.00,0.25,147,80),(163,'Danielle','Greene','DGREENE','011.44.1346.229268','1999-03-19','SA_REP',9500.00,0.15,147,80),(164,'Mattea','Marvins','MMARVINS','011.44.1346.329268','2000-01-24','SA_REP',7200.00,0.10,147,80),(165,'David','Lee','DLEE','011.44.1346.529268','2000-02-23','SA_REP',6800.00,0.10,147,80),(166,'Sundar','Ande','SANDE','011.44.1346.629268','2000-03-24','SA_REP',6400.00,0.10,147,80),(167,'Amit','Banda','ABANDA','011.44.1346.729268','2000-04-21','SA_REP',6200.00,0.10,147,80),(168,'Lisa','Ozer','LOZER','011.44.1343.929268','1997-03-11','SA_REP',11500.00,0.25,148,80),(169,'Harrison','Bloom','HBLOOM','011.44.1343.829268','1998-03-23','SA_REP',10000.00,0.20,148,80),(170,'Tayler','Fox','TFOX','011.44.1343.729268','1998-01-24','SA_REP',9600.00,0.20,148,80),(171,'William','Smith','WSMITH','011.44.1343.629268','1999-02-23','SA_REP',7400.00,0.15,148,80),(172,'Elizabeth','Bates','EBATES','011.44.1343.529268','1999-03-24','SA_REP',7300.00,0.15,148,80),(173,'Sundita','Kumar','SKUMAR','011.44.1343.329268','2000-04-21','SA_REP',6100.00,0.10,148,80),(174,'Ellen','Abel','EABEL','011.44.1644.429267','1996-05-11','SA_REP',11000.00,0.30,149,80),(175,'Alyssa','Hutton','AHUTTON','011.44.1644.429266','1997-03-19','SA_REP',8800.00,0.25,149,80),(176,'Jonathon','Taylor','JTAYLOR','011.44.1644.429265','1998-03-24','SA_REP',8600.00,0.20,149,80),(177,'Jack','Livingston','JLIVINGS','011.44.1644.429264','1998-04-23','SA_REP',8400.00,0.20,149,80),(178,'Kimberely','Grant','KGRANT','011.44.1644.429263','1999-05-24','SA_REP',7000.00,0.15,149,NULL),(179,'Charles','Johnson','CJOHNSON','011.44.1644.429262','2000-01-04','SA_REP',6200.00,0.10,149,80),(180,'Winston','Taylor','WTAYLOR','650.507.9876','1998-01-24','SH_CLERK',3200.00,NULL,120,50),(181,'Jean','Fleaur','JFLEAUR','650.507.9877','1998-02-23','SH_CLERK',3100.00,NULL,120,50),(182,'Martha','Sullivan','MSULLIVA','650.507.9878','1999-06-21','SH_CLERK',2500.00,NULL,120,50),(183,'Girard','Geoni','GGEONI','650.507.9879','2000-02-03','SH_CLERK',2800.00,NULL,120,50),(184,'Nandita','Sarchand','NSARCHAN','650.509.1876','1996-01-27','SH_CLERK',4200.00,NULL,121,50),(185,'Alexis','Bull','ABULL','650.509.2876','1997-02-20','SH_CLERK',4100.00,NULL,121,50),(186,'Julia','Dellinger','JDELLING','650.509.3876','1998-06-24','SH_CLERK',3400.00,NULL,121,50),(187,'Anthony','Cabrio','ACABRIO','650.509.4876','1999-02-07','SH_CLERK',3000.00,NULL,121,50),(188,'Kelly','Chung','KCHUNG','650.505.1876','1997-06-14','SH_CLERK',3800.00,NULL,122,50),(189,'Jennifer','Dilly','JDILLY','650.505.2876','1997-08-13','SH_CLERK',3600.00,NULL,122,50),(190,'Timothy','Gates','TGATES','650.505.3876','1998-07-11','SH_CLERK',2900.00,NULL,122,50),(191,'Randall','Perkins','RPERKINS','650.505.4876','1999-12-19','SH_CLERK',2500.00,NULL,122,50),(192,'Sarah','Bell','SBELL','650.501.1876','1996-02-04','SH_CLERK',4000.00,NULL,123,50),(193,'Britney','Everett','BEVERETT','650.501.2876','1997-03-03','SH_CLERK',3900.00,NULL,123,50),(194,'Samuel','McCain','SMCCAIN','650.501.3876','1998-07-01','SH_CLERK',3200.00,NULL,123,50),(195,'Vance','Jones','VJONES','650.501.4876','1999-03-17','SH_CLERK',2800.00,NULL,123,50),(196,'Alana','Walsh','AWALSH','650.507.9811','1998-04-24','SH_CLERK',3100.00,NULL,124,50),(197,'Kevin','Feeney','KFEENEY','650.507.9822','1998-05-23','SH_CLERK',3000.00,NULL,124,50),(198,'Donald','OConnell','DOCONNEL','650.507.9833','1999-06-21','SH_CLERK',2600.00,NULL,124,50),(199,'Douglas','Grant','DGRANT','650.507.9844','2000-01-13','SH_CLERK',2600.00,NULL,124,50),(200,'Jennifer','Whalen','JWHALEN','515.123.4444','1987-09-17','AD_ASST',4400.00,NULL,101,10),(201,'Michael','Hartstein','MHARTSTE','515.123.5555','1996-02-17','MK_MAN',13000.00,NULL,100,20),(202,'Pat','Fay','PFAY','603.123.6666','1997-08-17','MK_REP',6000.00,NULL,201,20),(203,'Susan','Mavris','SMAVRIS','515.123.7777','1994-06-07','HR_REP',6500.00,NULL,101,40),(204,'Hermann','Baer','HBAER','515.123.8888','1994-06-07','PR_REP',10000.00,NULL,101,70),(205,'Shelley','Higgins','SHIGGINS','515.123.8080','1994-06-07','AC_MGR',12000.00,NULL,101,110),(206,'William','Gietz','WGIETZ','515.123.8181','1994-06-07','AC_ACCOUNT',8300.00,NULL,205,110);

/*Table structure for table `job_grades` */

DROP TABLE IF EXISTS `job_grades`;

CREATE TABLE `job_grades` (
  `grade_level` varchar(3) DEFAULT NULL,
  `lowest_sal` int(11) DEFAULT NULL,
  `highest_sal` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `job_grades` */

insert  into `job_grades`(`grade_level`,`lowest_sal`,`highest_sal`) values ('A',1000,2999),('B',3000,5999),('C',6000,9999),('D',10000,14999),('E',15000,24999),('F',25000,40000);

/*Table structure for table `job_history` */

DROP TABLE IF EXISTS `job_history`;

CREATE TABLE `job_history` (
  `employee_id` int(6) NOT NULL,
  `start_date` date NOT NULL,
  `end_date` date NOT NULL,
  `job_id` varchar(10) NOT NULL,
  `department_id` int(4) DEFAULT NULL,
  PRIMARY KEY (`employee_id`,`start_date`),
  UNIQUE KEY `jhist_emp_id_st_date_pk` (`employee_id`,`start_date`),
  KEY `jhist_job_fk` (`job_id`),
  KEY `jhist_dept_fk` (`department_id`),
  CONSTRAINT `jhist_dept_fk` FOREIGN KEY (`department_id`) REFERENCES `departments` (`department_id`),
  CONSTRAINT `jhist_emp_fk` FOREIGN KEY (`employee_id`) REFERENCES `employees` (`employee_id`),
  CONSTRAINT `jhist_job_fk` FOREIGN KEY (`job_id`) REFERENCES `jobs` (`job_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `job_history` */

insert  into `job_history`(`employee_id`,`start_date`,`end_date`,`job_id`,`department_id`) values (101,'1989-09-21','1993-10-27','AC_ACCOUNT',110),(101,'1993-10-28','1997-03-15','AC_MGR',110),(102,'1993-01-13','1998-07-24','IT_PROG',60),(114,'1998-03-24','1999-12-31','ST_CLERK',50),(122,'1999-01-01','1999-12-31','ST_CLERK',50),(176,'1998-03-24','1998-12-31','SA_REP',80),(176,'1999-01-01','1999-12-31','SA_MAN',80),(200,'1987-09-17','1993-06-17','AD_ASST',90),(200,'1994-07-01','1998-12-31','AC_ACCOUNT',90),(201,'1996-02-17','1999-12-19','MK_REP',20);

/*Table structure for table `jobs` */

DROP TABLE IF EXISTS `jobs`;

CREATE TABLE `jobs` (
  `job_id` varchar(10) NOT NULL DEFAULT '',
  `job_title` varchar(35) NOT NULL,
  `min_salary` int(6) DEFAULT NULL,
  `max_salary` int(6) DEFAULT NULL,
  PRIMARY KEY (`job_id`),
  UNIQUE KEY `job_id_pk` (`job_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `jobs` */

insert  into `jobs`(`job_id`,`job_title`,`min_salary`,`max_salary`) values ('AC_ACCOUNT','Public Accountant',4200,9000),('AC_MGR','Accounting Manager',8200,16000),('AD_ASST','Administration Assistant',3000,6000),('AD_PRES','President',20000,40000),('AD_VP','Administration Vice President',15000,30000),('FI_ACCOUNT','Accountant',4200,9000),('FI_MGR','Finance Manager',8200,16000),('HR_REP','Human Resources Representative',4000,9000),('IT_PROG','Programmer',4000,10000),('MK_MAN','Marketing Manager',9000,15000),('MK_REP','Marketing Representative',4000,9000),('PR_REP','Public Relations Representative',4500,10500),('PU_CLERK','Purchasing Clerk',2500,5500),('PU_MAN','Purchasing Manager',8000,15000),('SA_MAN','Sales Manager',10000,20000),('SA_REP','Sales Representative',6000,12000),('SH_CLERK','Shipping Clerk',2500,5500),('ST_CLERK','Stock Clerk',2000,5000),('ST_MAN','Stock Manager',5500,8500);

/*Table structure for table `locations` */

DROP TABLE IF EXISTS `locations`;

CREATE TABLE `locations` (
  `location_id` int(4) NOT NULL DEFAULT '0',
  `street_address` varchar(40) DEFAULT NULL,
  `postal_code` varchar(12) DEFAULT NULL,
  `city` varchar(30) NOT NULL,
  `state_province` varchar(25) DEFAULT NULL,
  `country_id` char(2) DEFAULT NULL,
  PRIMARY KEY (`location_id`),
  UNIQUE KEY `loc_id_pk` (`location_id`),
  KEY `loc_c_id_fk` (`country_id`),
  CONSTRAINT `loc_c_id_fk` FOREIGN KEY (`country_id`) REFERENCES `countries` (`country_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `locations` */

insert  into `locations`(`location_id`,`street_address`,`postal_code`,`city`,`state_province`,`country_id`) values (1000,'1297 Via Cola di Rie','00989','Roma',NULL,'IT'),(1100,'93091 Calle della Testa','10934','Venice',NULL,'IT'),(1200,'2017 Shinjuku-ku','1689','Tokyo','Tokyo Prefecture','JP'),(1300,'9450 Kamiya-cho','6823','Hiroshima',NULL,'JP'),(1400,'2014 Jabberwocky Rd','26192','Southlake','Texas','US'),(1500,'2011 Interiors Blvd','99236','South San Francisco','California','US'),(1600,'2007 Zagora St','50090','South Brunswick','New Jersey','US'),(1700,'2004 Charade Rd','98199','Seattle','Washington','US'),(1800,'147 Spadina Ave','M5V 2L7','Toronto','Ontario','CA'),(1900,'6092 Boxwood St','YSW 9T2','Whitehorse','Yukon','CA'),(2000,'40-5-12 Laogianggen','190518','Beijing',NULL,'CN'),(2100,'1298 Vileparle (E)','490231','Bombay','Maharashtra','IN'),(2200,'12-98 Victoria Street','2901','Sydney','New South Wales','AU'),(2300,'198 Clementi North','540198','Singapore',NULL,'SG'),(2400,'8204 Arthur St',NULL,'London',NULL,'UK'),(2500,'Magdalen Centre, The Oxford Science Park','OX9 9ZB','Oxford','Oxford','UK'),(2600,'9702 Chester Road','09629850293','Stretford','Manchester','UK'),(2700,'Schwanthalerstr. 7031','80925','Munich','Bavaria','DE'),(2800,'Rua Frei Caneca 1360 ','01307-002','Sao Paulo','Sao Paulo','BR'),(2900,'20 Rue des Corps-Saints','1730','Geneva','Geneve','CH'),(3000,'Murtenstrasse 921','3095','Bern','BE','CH'),(3100,'Pieter Breughelstraat 837','3029SK','Utrecht','Utrecht','NL'),(3200,'Mariano Escobedo 9991','11932','Mexico City','Distrito Federal,','MX');

/*Table structure for table `order` */

DROP TABLE IF EXISTS `order`;

CREATE TABLE `order` (
  `order_id` int(11) DEFAULT NULL,
  `order_name` varchar(15) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `order` */

insert  into `order`(`order_id`,`order_name`) values (1,'shkstart'),(2,'tomcat'),(3,'dubbo');

/*Table structure for table `regions` */

DROP TABLE IF EXISTS `regions`;

CREATE TABLE `regions` (
  `region_id` int(11) NOT NULL,
  `region_name` varchar(25) DEFAULT NULL,
  PRIMARY KEY (`region_id`),
  UNIQUE KEY `reg_id_pk` (`region_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*Data for the table `regions` */

insert  into `regions`(`region_id`,`region_name`) values (1,'Europe'),(2,'Americas'),(3,'Asia'),(4,'Middle East and Africa');

/*Table structure for table `emp_details_view` */

DROP TABLE IF EXISTS `emp_details_view`;

/*!50001 DROP VIEW IF EXISTS `emp_details_view` */;
/*!50001 DROP TABLE IF EXISTS `emp_details_view` */;

/*!50001 CREATE TABLE  `emp_details_view`(
 `employee_id` int(6) ,
 `job_id` varchar(10) ,
 `manager_id` int(6) ,
 `department_id` int(4) ,
 `location_id` int(4) ,
 `country_id` char(2) ,
 `first_name` varchar(20) ,
 `last_name` varchar(25) ,
 `salary` double(8,2) ,
 `commission_pct` double(2,2) ,
 `department_name` varchar(30) ,
 `job_title` varchar(35) ,
 `city` varchar(30) ,
 `state_province` varchar(25) ,
 `country_name` varchar(40) ,
 `region_name` varchar(25) 
)*/;

/*View structure for view emp_details_view */

/*!50001 DROP TABLE IF EXISTS `emp_details_view` */;
/*!50001 DROP VIEW IF EXISTS `emp_details_view` */;

/*!50001 CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `emp_details_view` AS select `e`.`employee_id` AS `employee_id`,`e`.`job_id` AS `job_id`,`e`.`manager_id` AS `manager_id`,`e`.`department_id` AS `department_id`,`d`.`location_id` AS `location_id`,`l`.`country_id` AS `country_id`,`e`.`first_name` AS `first_name`,`e`.`last_name` AS `last_name`,`e`.`salary` AS `salary`,`e`.`commission_pct` AS `commission_pct`,`d`.`department_name` AS `department_name`,`j`.`job_title` AS `job_title`,`l`.`city` AS `city`,`l`.`state_province` AS `state_province`,`c`.`country_name` AS `country_name`,`r`.`region_name` AS `region_name` from (((((`employees` `e` join `departments` `d`) join `jobs` `j`) join `locations` `l`) join `countries` `c`) join `regions` `r`) where ((`e`.`department_id` = `d`.`department_id`) and (`d`.`location_id` = `l`.`location_id`) and (`l`.`country_id` = `c`.`country_id`) and (`c`.`region_id` = `r`.`region_id`) and (`j`.`job_id` = `e`.`job_id`)) */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

    mysql> source /var/lib/mysql/tmp/atguigudb.sql;
mysql> USE atguigudb;
Database changed
mysql> SHOW TABLES;
+---------------------+
| Tables_in_atguigudb |
+---------------------+
| countries           |
| departments         |
| emp_details_view    |
| employees           |
| job_grades          |
| job_history         |
| jobs                |
| locations           |
| order               |
| regions             |
+---------------------+
10 rows in set (0.01 sec)

  • 查看全部的数据库：SHOW DATABASES;。

    mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| atguigudb          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

    • information_schema、performance_schema、sys和mysql，都是 MySQL 系统自带的数据库。

    • information_schema库主要保存 MySQL 数据库服务器的系统信息，比如数据库的名称、数据表的名称、字段名称、存取权限、数据文件所在的文件夹和系统使用的文件夹，等等。

    • performance_schema库可以用来监控 MySQL 的各类性能指标。

    • sys库主要作用是以一种更容易被理解的方式，展示 MySQL 数据库服务器的各类性能指标，帮助系统管理员和开发人员监控 MySQL 的技术性能。

    • mysql库保存了 MySQL 数据库服务器运行时需要的系统信息，比如数据文件夹、当前使用的字符集、约束检查信息，等等。

  • 创建数据库：CREATE DATABASES [数据库名];。

    mysql> CREATE DATABASES test;
Query OK, 1 row affected (0.02 sec)

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| atguigudb          |
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
+--------------------+
6 rows in set (0.00 sec)

  • 使用数据库：USE [数据库名];。

    mysql> USE test;
Database changed

    • 如果没有使用 USE 语句，对数据库的操作也没有加 "数据名" 的限定，那么会报 "ERROR 1046(3D000): No database selected"（没有选择数据库）。

    • 使用完 USE 语句之后，如果接下来的 SQL 都是针对一个数据库操作的，那就不用重复 USE 了，如果要针对另一个数据库操作，那么要重新 USE。

  • 查看当前数据库中有哪些数据表：SHOW TABLES;。

    mysql> SHOW TABLES;
Empty set (0.00 sec)

  • 查看指定数据库中有哪些数据表：SHOW TABLES FROM [数据库名];。

    mysql> SHOW TABLES FROM atguigudb;
+---------------------+
| Tables_in_atguigudb |
+---------------------+
| countries           |
| departments         |
| emp_details_view    |
| employees           |
| job_grades          |
| job_history         |
| jobs                |
| locations           |
| order               |
| regions             |
+---------------------+
10 rows in set (0.00 sec)

  • 建表：CREATE TABLE [表名(表结构)];。

    mysql> CREATE TABLE student (
    ->   id int,
    ->   name varchar(20)
    -> );
Query OK, 0 rows affected (0.04 sec)
mysql> SHOW TABLES;
+----------------+
| Tables_in_test |
+----------------+
| student        |
+----------------+
1 row in set (0.00 sec)
    • 如果是最后一个字段，后面就不用加逗号，因为逗号的作用是分割每个字段。

  • 查看表结构：DESC[RIBE] [表名];，或者SHOW FULL COLUMNS FROM [表名];。

    mysql> DESC student;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int         | YES  |     | NULL    |       |
| name  | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)

mysql> SHOW FULL COLUMNS FROM student;
+-------+-------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type        | Collation          | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+-------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
| id    | int         | NULL               | YES  |     | NULL    |       | select,insert,update,references |         |
| name  | varchar(20) | utf8mb4_0900_ai_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+-------------+--------------------+------+-----+---------+-------+---------------------------------+---------+
2 rows in set (0.00 sec)

    • Field：表示字段名称。

    • Type：表示字段类型。

    • Null：表示该列是否可以存储 NULL 值。

    • Key：表示该列是否已编制索引。PRI 值表示该列是表主键的一部分；UNI 值表示该列是 UNIQUE 索引的一部分；MUL 值表示在列中某个给定值允许出现多次。

    • Default：表示该列是否有默认值，如果有，那么值是多少。

    • Extra：表示可以获取的与给定列有关的附加信息，例如 AUTO_INCREMENT 等。

  • 查看表中的所有记录：SELECT * FROM [表名];。

    mysql> SELECT * FROM student;
Empty set (0.10 sec)

  • 向表中添加一条记录：INSERT INTO [表名 (表字段列表)] VALUES [(值列表)];。

    mysql> INSERT INTO student VALUES (1, 'Tom');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO student VALUES (1, 'Jerry');
Query OK, 1 row affected (0.01 sec)

  • 修改表中的记录：UPDATE [表名] SET [表字段1 = 值1, 表字段2 = 值2 ...] WHERE [条件];。

    mysql> UPDATE student SET id = 2 WHERE name = 'Jerry';
Query OK, 1 row affected (0.04 sec)
Rows matched: 1  Changed: 1  Warnings: 0

  • 删除表中的记录：DELETE FROM [表名] WHERE [条件];。

    mysql> DELETE FROM student WHERE id = 3;
Query OK, 1 row affected (0.01 sec)

  • 查看表的创建信息：SHOW CREATE TABLE [表名];。

    mysql> SHOW CREATE TABLE student;
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                           |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
  `id` int DEFAULT NULL,
  `name` varchar(20) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)-

  • 查看数据库的创建信息：SHOW CREATE DATABASES [数据库名];。

    mysql> SHOW CREATE DATABASE test;
+----------+--------------------------------------------------------------------------------------------------------------------------------+
| Database | Create Database                                                                                                                |
+----------+--------------------------------------------------------------------------------------------------------------------------------+
| test     | CREATE DATABASE `test` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci */ /*!80016 DEFAULT ENCRYPTION='N' */ |
+----------+--------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.05 sec)

  • 删除表：DROP TABLE [表名];。

    mysql> DROP TABLE student;
Query OK, 0 rows affected (0.32 sec)

  • 删除数据库：DROP DATABASE [数据库名];。

    mysql> DROP DATABASE test;
Query OK, 0 rows affected (0.13 sec)

MySQL 的编码

查看编码命令：

mysql> SHOW VARIABLES LIKE 'character_%';
+--------------------------+--------------------------------+
| Variable_name            | Value                          |
+--------------------------+--------------------------------+
| character_set_client     | latin1                         |
| character_set_connection | latin1                         |
| character_set_database   | utf8mb4                        |
| character_set_filesystem | binary                         |
| character_set_results    | latin1                         |
| character_set_server     | utf8mb4                        |
| character_set_system     | utf8mb3                        |
| character_sets_dir       | /usr/share/mysql-8.0/charsets/ |
+--------------------------+--------------------------------+
8 rows in set (0.00 sec)

mysql> SHOW VARIABLES LIKE 'collation_%';
+----------------------+--------------------+
| Variable_name        | Value              |
+----------------------+--------------------+
| collation_connection | latin1_swedish_ci  |
| collation_database   | utf8mb4_0900_ai_ci |
| collation_server     | utf8mb4_0900_ai_ci |
+----------------------+--------------------+
3 rows in set (0.00 sec)

在 MySQL 8.0 版本之前，默认字符集为latin1，utf8 字符集指向的是 utf8mb3。网站开发人员在数据库设计的时候往往会将编码修改为 utf8 字符集，如果遗忘修改默认的编码，就会出现乱码的问题。从 MySQL 8.0 开始，数据库的默认字符集为utf8mb4，从而避免了上述的乱码问题。

基本的 SELECT 语句

常规语法

SELECT [标识选择哪些列] FROM [标识从哪个表中选择];

查询所有列的所有数据：

mysql> SELECT * FROM employee;
+----+----------+--------+-----+--------+
| id | emp_name | sex    | age | dep_id |
+----+----------+--------+-----+--------+
|  1 | Tom      | male   |  27 |      1 |
|  2 | Jerry    | male   |  28 |      2 |
|  3 | Lucy     | female |  29 |      2 |
+----+----------+--------+-----+--------+
3 rows in set (0.00 sec)
  • 一般情况下，除非需要使用表中所有的字段数据，最好不要使用通配符*。使用通配符虽然可以节省输入查询语句的时间，但是获取不需要的列数据，通常会降低查询和所使用的应用程序的效率。
  • 通配符的优势是，当不知道所需要的列的名称时，可以通过它获取它们。
  • 在生产环境下，不推荐直接使用 SELECT * 进行查询。

查询特定列的所有数据：

mysql> SELECT emp_name, sex FROM employee;
+----------+--------+
| emp_name | sex    |
+----------+--------+
| Tom      | male   |
| Jerry    | male   |
| Lucy     | female |
+----------+--------+
3 rows in set (0.00 sec)

查询常数

SELECT 查询可以对常数进行查询，即在 SELECT 查询结果中增加一列固定的常数列，这列的取值是我们指定的，而不是从数据表中动态取出的。一般来说我们只从一个表中查询数据，通常不需要增加一个固定的常数列，但如果我们想整合不同的数据源，用常数列作为这个表的标记，就需要查询常数。

mysql> SELECT 1;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

mysql> SELECT 9/2;
+--------+
| 9/2    |
+--------+
| 4.5000 |
+--------+
1 row in set (0.00 sec)

mysql> SELECT 4*3;
+-----+
| 4*3 |
+-----+
|  12 |
+-----+
1 row in set (0.00 sec)

别名

语法：在表名或列名，与其别名之间加入关键字AS，如果别名中包含空格或特殊的字符或区分大小写，则别名使用双引号。

mysql> SELECT emp_name AS name, sex, age FROM employee;
+-------+--------+-----+
| name  | sex    | age |
+-------+--------+-----+
| Tom   | male   |  27 |
| Jerry | male   |  28 |
| Lucy  | female |  29 |
+-------+--------+-----+
3 rows in set (0.00 sec)

mysql> SELECT e.emp_name AS name, e.sex, e.age FROM employee e;
+-------+--------+-----+
| name  | sex    | age |
+-------+--------+-----+
| Tom   | male   |  27 |
| Jerry | male   |  28 |
| Lucy  | female |  29 |
+-------+--------+-----+
3 rows in set (0.01 sec)

AS 可以省略。

去除重复行

默认情况下，查询会返回全部行，包括重复行。在 SELECT 语句中使用关键字DISTINCT去除重复行。

mysql> SELECT DISTINCT dep_id FROM employee;
+--------+
| dep_id |
+--------+
|      1 |
|      2 |
+--------+
2 rows in set (0.00 sec)

DISTINCT 可以使用在多个字段上：

mysql> SELECT * FROM employee;
+----+----------+--------+-----+--------+
| id | emp_name | sex    | age | dep_id |
+----+----------+--------+-----+--------+
|  1 | Tom      | male   |  27 |      1 |
|  2 | Jerry    | male   |  28 |      2 |
|  3 | Lucy     | female |  29 |      2 |
|  4 | Lily     | female |  28 |      2 |
+----+----------+--------+-----+--------+
4 rows in set (0.00 sec)

mysql> SELECT DISTINCT sex FROM employee;
+--------+
| sex    |
+--------+
| male   |
| female |
+--------+
2 rows in set (0.07 sec)

mysql> SELECT DISTINCT sex, dep_id FROM employee;
+--------+--------+
| sex    | dep_id |
+--------+--------+
| male   |      1 |
| male   |      2 |
| female |      2 |
+--------+--------+
3 rows in set (0.00 sec)
  • DISTINCT 需要放到所有列名的前面。
  • 多个字段时，DISTINCT 依次从左至右去重。以 "SELECT DISTINCT sex, dep_id FROM employee;" 为例，先对 sex 去重，然后再对 dep_id 去重。

空值参与运算

所有运算符或列值遇到 null 值，运算的结果都为 null。注意，在 MySQL 中， 空值不等于空字符串。一个空字符串的长度是 0，而一个空值的长度是空。同时，在 MySQL 中，空值是占用空间的。

mysql> SELECT employee_id, salary, commission_pct, 12 * salary * (1 + commission_pct) "annual_sal" FROM employees;
+-------------+----------+----------------+------------+
| employee_id | salary   | commission_pct | annual_sal |
+-------------+----------+----------------+------------+
|         100 | 24000.00 |           NULL |       NULL |
|         101 | 17000.00 |           NULL |       NULL |
|         102 | 17000.00 |           NULL |       NULL |
|         145 | 14000.00 |           0.40 |  235200.00 |
|         146 | 13500.00 |           0.30 |  210600.00 |
|         147 | 12000.00 |           0.30 |  187200.00 |
+-------------+----------+----------------+------------+
6 rows in set (0.00 sec)

着重号

表中的字段、表名等，不应该和保留字、数据库系统或常用方法冲突。如果真的相同，需要在 SQL 语句中使用一对```（着重号）`引起来。

mysql> SELECT * FROM ORDER;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER' at line 1

mysql> SELECT * FROM `ORDER`;
+----------+------------+
| order_id | order_name |
+----------+------------+
| 1        | shkstart   |
| 2        | tomcat     |
| 3        | dubbo      |
+----------+------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM `order`;
+----------+------------+
| order_id | order_name |
+----------+------------+
| 1        | shkstart   |
| 2        | tomcat     |
| 3        | dubbo      |
+----------+------------+
3 rows in set (0.00 sec)

过滤

在 SELECT 语句中使用关键字WHERE去除重复行。

mysql> SELECT DISTINCT sex, dep_id FROM employee WHERE dep_id = 1;
+--------+--------+
| sex    | dep_id |
+--------+--------+
| male   | 1      |
+--------+--------+
1 rows in set (0.00 sec)
  • WHERE 子句紧随 FROM 子句。

排序

排序规则

MySQL 使用ORDER BY子句排序：

  • ASC（ascend）: 升序。

  • DESC（descend）：降序。

  • ORDER BY 子句在 SELECT 语句的结尾。

  • ORDER BY 子句，默认按照升序排序，如果不指定 ORDER BY 子句，默认按照数据添加的顺序排序。

单列排序

mysql> SELECT last_name, job_id, department_id, hire_date FROM employees ORDER BY hire_date;
+-------------+------------+---------------+------------+
| last_name   | job_id     | department_id | hire_date  |
+-------------+------------+---------------+------------+
| King        | AD_PRES    |            90 | 1987-06-17 |
| Whalen      | AD_ASST    |            10 | 1987-09-17 |
| Kochhar     | AD_VP      |            90 | 1989-09-21 |
+-------------+------------+---------------+------------+
3 rows in set (0.00 sec)

mysql> SELECT last_name, job_id, department_id, hire_date FROM employees ORDER BY hire_date DESC;
+-------------+------------+---------------+------------+
| last_name   | job_id     | department_id | hire_date  |
+-------------+------------+---------------+------------+
| Banda       | SA_REP     |            80 | 2000-04-21 |
| Kumar       | SA_REP     |            80 | 2000-04-21 |
| Ande        | SA_REP     |            80 | 2000-03-24 |
+-------------+------------+---------------+------------+
3 rows in set (0.00 sec)

mysql> SELECT employee_id, last_name, salary * 12 annsal FROM employees ORDER BY annsal;
+-------------+-------------+-----------+
| employee_id | last_name   | annsal    |
+-------------+-------------+-----------+
|         132 | Olson       |  25200.00 |
|         128 | Markle      |  26400.00 |
|         136 | Philtanker  |  26400.00 |
|         127 | Landry      |  28800.00 |
|         135 | Gee         |  28800.00 |
|         119 | Colmenares  |  30000.00 |
|         131 | Marlow      |  30000.00 |
|         140 | Patel       |  30000.00 |
|         144 | Vargas      |  30000.00 |
|         182 | Sullivan    |  30000.00 |
|         191 | Perkins     |  30000.00 |
+-------------+-------------+-----------+
11 rows in set (0.00 sec)

多列排序

mysql> SELECT last_name, department_id, salary FROM employees ORDER BY department_id, salary DESC;
+-------------+---------------+----------+
| last_name   | department_id | salary   |
+-------------+---------------+----------+
| Grant       |          NULL |  7000.00 |
| Whalen      |            10 |  4400.00 |
| Hartstein   |            20 | 13000.00 |
| Fay         |            20 |  6000.00 |
| Raphaely    |            30 | 11000.00 |
| Khoo        |            30 |  3100.00 |
| Baida       |            30 |  2900.00 |
| Tobias      |            30 |  2800.00 |
| Himuro      |            30 |  2600.00 |
| Colmenares  |            30 |  2500.00 |
+-------------+---------------+----------+
11 rows in set (0.00 sec)
  • 可以使用不在 SELECT 列表中的列排序。
  • 在对多列进行排序的时候，首先排序的第一列必须有相同的列值，才会对第二列进行排序。如果第一列数据中所有值都是唯一的，将不再对第二列进行排序。

分页

分页规则

分页原理：所谓分页显示，就是将数据库中的结果集，一段一段显示出来需要的条数。

MySQL 使用LIMIT子句分页，格式：

LIMIT [位置偏移量,] 行数

第一个参数 "位置偏移量" 指示 MySQL 从哪一行开始显示，是一个可选参数，如果不指定 "位置偏移量"，将会从表中的第一条记录开始（第一条记录的位置偏移量是 0，第二条记录的位置偏移量是 1，以此类推）；

第二个参数 "行数" 指示 MySQL 返回的记录条数。

# 前 10 条记录
mysql> SELECT * FROM 表名 LIMIT 0, 10;
或者
mysql> SELECT * FROM 表名 LIMIT 10;

# 第 11 至 20 条记录
mysql> SELECT * FROM 表名 LIMIT 10, 10;

# 第 21 至 30 条记录
mysql> SELECT * FROM 表名 LIMIT 20, 10;

MySQL 8.0 中可以使用LIMIT 3 OFFSET 4，意思是获取从第 5 条记录开始后面的 3 条记录，和LIMIT 4, 3;返回的结果相同。

分页公式

公式：(PageNo - 1) * PageSize, PageSize。

mysql> SELECT * FROM table LIMIT (PageNo - 1) * PageSize, PageSize;

LIMIT 子句必须放在整个 SELECT 语句的最后！

使用 LIMIT 的好处：约束返回结果的数量可以减少数据表的网络传输量，也可以提升查询效率。如果我们知道返回结果只有 1 条，就可以使用 LIMIT 1，告诉 SELECT 语句只需要返回一条记录即可，这样的好处就是 SELECT 不需要扫描完整的表，只需要检索到一条符合条件的记录即可返回。

分页拓展

在不同的 DBMS 中分页使用的关键字可能不同。在 MySQL、PostgreSQL、MariaDB 和 SQLite 中使用 LIMIT 关键字，而且需要放到 SELECT 语句的最后面。

如果是 SQL Server 和 Access，需要使用 TOP 关键字，比如：

SELECT TOP 5 name, hp_max FROM heros ORDER BY hp_max DESC;

如果是 DB2，使用 FETCH FIRST 5 ROWS ONLY 这样的关键字：

SELECT name, hp_max FROM heros ORDER BY hp_max DESC FETCH FIRST 5 ROWS ONLY;

如果是 Oracle，需要基于 ROWNUM 来统计行数：

SELECT rownum, last_name,s alary FROM employees WHERE rownum < 5 ORDER BY salary DESC;

原文链接

https://github.com/ACatSmiling/zero-to-zero/blob/main/RelationalDatabase/mysql.md

posted @ 2024-09-22 00:33  ACatSmiling  阅读(41)  评论(0)  编辑  收藏  举报