Mysql-04-DQL

字数统计: 7.9k字   |   阅读时长≈ 42分钟

Mysql-04-DQL

DQL语言

DQL( Data Query Language 数据查询语言 )

  • 查询数据库数据 , 如SELECT语句

  • 简单的单表查询或多表的复杂查询和嵌套查询

  • 使用频率最高的语句

  • 是数据库语言中最核心,最重要的语句

1. select 语法公式

1
2
3
4
5
6
7
8
9
10
11
12
/*
SELECT [ALL | DISTINCT]
{* | table.* | [table.field1[as alias1][,table.field2[as alias2]][,...]]}
FROM table_name [as table_alias]
    [left | right | inner join table_name2]  #联合查询
    [WHERE ...]  #指定结果需满足的条件
    [GROUP BY ...]  #指定结果按照哪几个字段来分组
    [HAVING]  #过滤分组的记录必须满足的次要条件
    [ORDER BY ...]  #指定查询记录按一个或多个条件排序
    [LIMIT {[offset,]row_count | row_countOFFSET offset}];
    # 指定查询的记录从哪条至哪条
*/

预备数据环境：提供的素材SQL语句 : 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
/*
SQLyog Ultimate v10.00 Beta1
MySQL - 5.7.19 : Database - school
*********************************************************************
*/


/*!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*/`school` /*!40100 DEFAULT CHARACTER SET utf8 */;

USE `school`;

/*Table structure for table `grade` */

DROP TABLE IF EXISTS `grade`;

CREATE TABLE `grade` (
  `GradeID` INT(11) NOT NULL AUTO_INCREMENT COMMENT '年级编号',
  `GradeName` VARCHAR(50) NOT NULL COMMENT '年级名称',
  PRIMARY KEY (`GradeID`)
) ENGINE=INNODB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

/*Data for the table `grade` */

INSERT  INTO `grade`(`GradeID`,`GradeName`) VALUES (1,'大一'),(2,'大二'),(3,'大三'),(4,'大四'),(5,'预科班');

/*Table structure for table `result` */

DROP TABLE IF EXISTS `result`;

CREATE TABLE `result` (
  `StudentNo` INT(4) NOT NULL COMMENT '学号',
  `SubjectNo` INT(4) NOT NULL COMMENT '课程编号',
  `ExamDate` DATETIME NOT NULL COMMENT '考试日期',
  `StudentResult` INT(4) NOT NULL COMMENT '考试成绩',
  KEY `SubjectNo` (`SubjectNo`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

/*Data for the table `result` */

INSERT  INTO `result`(`StudentNo`,`SubjectNo`,`ExamDate`,`StudentResult`) VALUES (1000,1,'2013-11-11 16:00:00',94),(1000,2,'2012-11-10 10:00:00',75),(1000,3,'2011-12-19 10:00:00',76),(1000,4,'2010-11-18 11:00:00',93),(1000,5,'2013-11-11 14:00:00',97),(1000,6,'2012-09-13 15:00:00',87),(1000,7,'2011-10-16 16:00:00',79),(1000,8,'2010-11-11 16:00:00',74),(1000,9,'2013-11-21 10:00:00',69),(1000,10,'2012-11-11 12:00:00',78),(1000,11,'2011-11-11 14:00:00',66),(1000,12,'2010-11-11 15:00:00',82),(1000,13,'2013-11-11 14:00:00',94),(1000,14,'2012-11-11 15:00:00',98),(1000,15,'2011-12-11 10:00:00',70),(1000,16,'2010-09-11 10:00:00',74),(1001,1,'2013-11-11 16:00:00',76),(1001,2,'2012-11-10 10:00:00',93),(1001,3,'2011-12-19 10:00:00',65),(1001,4,'2010-11-18 11:00:00',71),(1001,5,'2013-11-11 14:00:00',98),(1001,6,'2012-09-13 15:00:00',74),(1001,7,'2011-10-16 16:00:00',85),(1001,8,'2010-11-11 16:00:00',69),(1001,9,'2013-11-21 10:00:00',63),(1001,10,'2012-11-11 12:00:00',70),(1001,11,'2011-11-11 14:00:00',62),(1001,12,'2010-11-11 15:00:00',90),(1001,13,'2013-11-11 14:00:00',97),(1001,14,'2012-11-11 15:00:00',89),(1001,15,'2011-12-11 10:00:00',72),(1001,16,'2010-09-11 10:00:00',90),(1002,1,'2013-11-11 16:00:00',61),(1002,2,'2012-11-10 10:00:00',80),(1002,3,'2011-12-19 10:00:00',89),(1002,4,'2010-11-18 11:00:00',88),(1002,5,'2013-11-11 14:00:00',82),(1002,6,'2012-09-13 15:00:00',91),(1002,7,'2011-10-16 16:00:00',63),(1002,8,'2010-11-11 16:00:00',84),(1002,9,'2013-11-21 10:00:00',60),(1002,10,'2012-11-11 12:00:00',71),(1002,11,'2011-11-11 14:00:00',93),(1002,12,'2010-11-11 15:00:00',96),(1002,13,'2013-11-11 14:00:00',83),(1002,14,'2012-11-11 15:00:00',69),(1002,15,'2011-12-11 10:00:00',89),(1002,16,'2010-09-11 10:00:00',83),(1003,1,'2013-11-11 16:00:00',91),(1003,2,'2012-11-10 10:00:00',75),(1003,3,'2011-12-19 10:00:00',65),(1003,4,'2010-11-18 11:00:00',63),(1003,5,'2013-11-11 14:00:00',90),(1003,6,'2012-09-13 15:00:00',96),(1003,7,'2011-10-16 16:00:00',97),(1003,8,'2010-11-11 16:00:00',77),(1003,9,'2013-11-21 10:00:00',62),(1003,10,'2012-11-11 12:00:00',81),(1003,11,'2011-11-11 14:00:00',76),(1003,12,'2010-11-11 15:00:00',61),(1003,13,'2013-11-11 14:00:00',93),(1003,14,'2012-11-11 15:00:00',79),(1003,15,'2011-12-11 10:00:00',78),(1003,16,'2010-09-11 10:00:00',96),(1004,1,'2013-11-11 16:00:00',84),(1004,2,'2012-11-10 10:00:00',79),(1004,3,'2011-12-19 10:00:00',76),(1004,4,'2010-11-18 11:00:00',78),(1004,5,'2013-11-11 14:00:00',81),(1004,6,'2012-09-13 15:00:00',90),(1004,7,'2011-10-16 16:00:00',63),(1004,8,'2010-11-11 16:00:00',89),(1004,9,'2013-11-21 10:00:00',67),(1004,10,'2012-11-11 12:00:00',100),(1004,11,'2011-11-11 14:00:00',94),(1004,12,'2010-11-11 15:00:00',65),(1004,13,'2013-11-11 14:00:00',86),(1004,14,'2012-11-11 15:00:00',77),(1004,15,'2011-12-11 10:00:00',82),(1004,16,'2010-09-11 10:00:00',87),(1005,1,'2013-11-11 16:00:00',82),(1005,2,'2012-11-10 10:00:00',92),(1005,3,'2011-12-19 10:00:00',80),(1005,4,'2010-11-18 11:00:00',92),(1005,5,'2013-11-11 14:00:00',97),(1005,6,'2012-09-13 15:00:00',72),(1005,7,'2011-10-16 16:00:00',84),(1005,8,'2010-11-11 16:00:00',79),(1005,9,'2013-11-21 10:00:00',76),(1005,10,'2012-11-11 12:00:00',87),(1005,11,'2011-11-11 14:00:00',65),(1005,12,'2010-11-11 15:00:00',67),(1005,13,'2013-11-11 14:00:00',63),(1005,14,'2012-11-11 15:00:00',64),(1005,15,'2011-12-11 10:00:00',99),(1005,16,'2010-09-11 10:00:00',97),(1006,1,'2013-11-11 16:00:00',82),(1006,2,'2012-11-10 10:00:00',73),(1006,3,'2011-12-19 10:00:00',79),(1006,4,'2010-11-18 11:00:00',63),(1006,5,'2013-11-11 14:00:00',97),(1006,6,'2012-09-13 15:00:00',83),(1006,7,'2011-10-16 16:00:00',78),(1006,8,'2010-11-11 16:00:00',88),(1006,9,'2013-11-21 10:00:00',89),(1006,10,'2012-11-11 12:00:00',82),(1006,11,'2011-11-11 14:00:00',70),(1006,12,'2010-11-11 15:00:00',69),(1006,13,'2013-11-11 14:00:00',64),(1006,14,'2012-11-11 15:00:00',80),(1006,15,'2011-12-11 10:00:00',90),(1006,16,'2010-09-11 10:00:00',85),(1007,1,'2013-11-11 16:00:00',87),(1007,2,'2012-11-10 10:00:00',63),(1007,3,'2011-12-19 10:00:00',70),(1007,4,'2010-11-18 11:00:00',74),(1007,5,'2013-11-11 14:00:00',79),(1007,6,'2012-09-13 15:00:00',83),(1007,7,'2011-10-16 16:00:00',86),(1007,8,'2010-11-11 16:00:00',76),(1007,9,'2013-11-21 10:00:00',65),(1007,10,'2012-11-11 12:00:00',87),(1007,11,'2011-11-11 14:00:00',69),(1007,12,'2010-11-11 15:00:00',69),(1007,13,'2013-11-11 14:00:00',90),(1007,14,'2012-11-11 15:00:00',84),(1007,15,'2011-12-11 10:00:00',95),(1007,16,'2010-09-11 10:00:00',92),(1008,1,'2013-11-11 16:00:00',96),(1008,2,'2012-11-10 10:00:00',62),(1008,3,'2011-12-19 10:00:00',97),(1008,4,'2010-11-18 11:00:00',84),(1008,5,'2013-11-11 14:00:00',86),(1008,6,'2012-09-13 15:00:00',72),(1008,7,'2011-10-16 16:00:00',67),(1008,8,'2010-11-11 16:00:00',83),(1008,9,'2013-11-21 10:00:00',86),(1008,10,'2012-11-11 12:00:00',60),(1008,11,'2011-11-11 14:00:00',61),(1008,12,'2010-11-11 15:00:00',68),(1008,13,'2013-11-11 14:00:00',99),(1008,14,'2012-11-11 15:00:00',77),(1008,15,'2011-12-11 10:00:00',73),(1008,16,'2010-09-11 10:00:00',78),(1009,1,'2013-11-11 16:00:00',67),(1009,2,'2012-11-10 10:00:00',70),(1009,3,'2011-12-19 10:00:00',75),(1009,4,'2010-11-18 11:00:00',92),(1009,5,'2013-11-11 14:00:00',76),(1009,6,'2012-09-13 15:00:00',90),(1009,7,'2011-10-16 16:00:00',62),(1009,8,'2010-11-11 16:00:00',68),(1009,9,'2013-11-21 10:00:00',70),(1009,10,'2012-11-11 12:00:00',83),(1009,11,'2011-11-11 14:00:00',88),(1009,12,'2010-11-11 15:00:00',65),(1009,13,'2013-11-11 14:00:00',91),(1009,14,'2012-11-11 15:00:00',99),(1009,15,'2011-12-11 10:00:00',65),(1009,16,'2010-09-11 10:00:00',83),(1010,1,'2013-11-11 16:00:00',83),(1010,2,'2012-11-10 10:00:00',87),(1010,3,'2011-12-19 10:00:00',89),(1010,4,'2010-11-18 11:00:00',99),(1010,5,'2013-11-11 14:00:00',91),(1010,6,'2012-09-13 15:00:00',96),(1010,7,'2011-10-16 16:00:00',72),(1010,8,'2010-11-11 16:00:00',72),(1010,9,'2013-11-21 10:00:00',98),(1010,10,'2012-11-11 12:00:00',73),(1010,11,'2011-11-11 14:00:00',68),(1010,12,'2010-11-11 15:00:00',62),(1010,13,'2013-11-11 14:00:00',67),(1010,14,'2012-11-11 15:00:00',69),(1010,15,'2011-12-11 10:00:00',71),(1010,16,'2010-09-11 10:00:00',66),(1011,1,'2013-11-11 16:00:00',62),(1011,2,'2012-11-10 10:00:00',72),(1011,3,'2011-12-19 10:00:00',96),(1011,4,'2010-11-18 11:00:00',64),(1011,5,'2013-11-11 14:00:00',89),(1011,6,'2012-09-13 15:00:00',91),(1011,7,'2011-10-16 16:00:00',95),(1011,8,'2010-11-11 16:00:00',96),(1011,9,'2013-11-21 10:00:00',89),(1011,10,'2012-11-11 12:00:00',73),(1011,11,'2011-11-11 14:00:00',82),(1011,12,'2010-11-11 15:00:00',98),(1011,13,'2013-11-11 14:00:00',66),(1011,14,'2012-11-11 15:00:00',69),(1011,15,'2011-12-11 10:00:00',91),(1011,16,'2010-09-11 10:00:00',69),(1012,1,'2013-11-11 16:00:00',86),(1012,2,'2012-11-10 10:00:00',66),(1012,3,'2011-12-19 10:00:00',97),(1012,4,'2010-11-18 11:00:00',69),(1012,5,'2013-11-11 14:00:00',70),(1012,6,'2012-09-13 15:00:00',74),(1012,7,'2011-10-16 16:00:00',91),(1012,8,'2010-11-11 16:00:00',97),(1012,9,'2013-11-21 10:00:00',84),(1012,10,'2012-11-11 12:00:00',82),(1012,11,'2011-11-11 14:00:00',90),(1012,12,'2010-11-11 15:00:00',91),(1012,13,'2013-11-11 14:00:00',91),(1012,14,'2012-11-11 15:00:00',97),(1012,15,'2011-12-11 10:00:00',85),(1012,16,'2010-09-11 10:00:00',90),(1013,1,'2013-11-11 16:00:00',73),(1013,2,'2012-11-10 10:00:00',69),(1013,3,'2011-12-19 10:00:00',91),(1013,4,'2010-11-18 11:00:00',72),(1013,5,'2013-11-11 14:00:00',76),(1013,6,'2012-09-13 15:00:00',87),(1013,7,'2011-10-16 16:00:00',61),(1013,8,'2010-11-11 16:00:00',77),(1013,9,'2013-11-21 10:00:00',83),(1013,10,'2012-11-11 12:00:00',99),(1013,11,'2011-11-11 14:00:00',91),(1013,12,'2010-11-11 15:00:00',84),(1013,13,'2013-11-11 14:00:00',98),(1013,14,'2012-11-11 15:00:00',74),(1013,15,'2011-12-11 10:00:00',92),(1013,16,'2010-09-11 10:00:00',90),(1014,1,'2013-11-11 16:00:00',64),(1014,2,'2012-11-10 10:00:00',81),(1014,3,'2011-12-19 10:00:00',79),(1014,4,'2010-11-18 11:00:00',74),(1014,5,'2013-11-11 14:00:00',65),(1014,6,'2012-09-13 15:00:00',88),(1014,7,'2011-10-16 16:00:00',86),(1014,8,'2010-11-11 16:00:00',77),(1014,9,'2013-11-21 10:00:00',86),(1014,10,'2012-11-11 12:00:00',85),(1014,11,'2011-11-11 14:00:00',86),(1014,12,'2010-11-11 15:00:00',75),(1014,13,'2013-11-11 14:00:00',89),(1014,14,'2012-11-11 15:00:00',79),(1014,15,'2011-12-11 10:00:00',73),(1014,16,'2010-09-11 10:00:00',68),(1015,1,'2013-11-11 16:00:00',99),(1015,2,'2012-11-10 10:00:00',60),(1015,3,'2011-12-19 10:00:00',60),(1015,4,'2010-11-18 11:00:00',75),(1015,5,'2013-11-11 14:00:00',78),(1015,6,'2012-09-13 15:00:00',78),(1015,7,'2011-10-16 16:00:00',84),(1015,8,'2010-11-11 16:00:00',95),(1015,9,'2013-11-21 10:00:00',93),(1015,10,'2012-11-11 12:00:00',79),(1015,11,'2011-11-11 14:00:00',74),(1015,12,'2010-11-11 15:00:00',65),(1015,13,'2013-11-11 14:00:00',63),(1015,14,'2012-11-11 15:00:00',74),(1015,15,'2011-12-11 10:00:00',67),(1015,16,'2010-09-11 10:00:00',65),(1016,1,'2013-11-11 16:00:00',97),(1016,2,'2012-11-10 10:00:00',90),(1016,3,'2011-12-19 10:00:00',77),(1016,4,'2010-11-18 11:00:00',75),(1016,5,'2013-11-11 14:00:00',75),(1016,6,'2012-09-13 15:00:00',97),(1016,7,'2011-10-16 16:00:00',96),(1016,8,'2010-11-11 16:00:00',92),(1016,9,'2013-11-21 10:00:00',62),(1016,10,'2012-11-11 12:00:00',83),(1016,11,'2011-11-11 14:00:00',98),(1016,12,'2010-11-11 15:00:00',94),(1016,13,'2013-11-11 14:00:00',62),(1016,14,'2012-11-11 15:00:00',97),(1016,15,'2011-12-11 10:00:00',76),(1016,16,'2010-09-11 10:00:00',82),(1017,1,'2013-11-11 16:00:00',100),(1017,2,'2012-11-10 10:00:00',88),(1017,3,'2011-12-19 10:00:00',86),(1017,4,'2010-11-18 11:00:00',73),(1017,5,'2013-11-11 14:00:00',96),(1017,6,'2012-09-13 15:00:00',64),(1017,7,'2011-10-16 16:00:00',81),(1017,8,'2010-11-11 16:00:00',66),(1017,9,'2013-11-21 10:00:00',76),(1017,10,'2012-11-11 12:00:00',95),(1017,11,'2011-11-11 14:00:00',73),(1017,12,'2010-11-11 15:00:00',82),(1017,13,'2013-11-11 14:00:00',85),(1017,14,'2012-11-11 15:00:00',68),(1017,15,'2011-12-11 10:00:00',99),(1017,16,'2010-09-11 10:00:00',76);

/*Table structure for table `student` */

DROP TABLE IF EXISTS `student`;

CREATE TABLE `student` (
  `StudentNo` INT(4) NOT NULL COMMENT '学号',
  `LoginPwd` VARCHAR(20) DEFAULT NULL,
  `StudentName` VARCHAR(20) DEFAULT NULL COMMENT '学生姓名',
  `Sex` TINYINT(1) DEFAULT NULL COMMENT '性别，取值0或1',
  `GradeId` INT(11) DEFAULT NULL COMMENT '年级编号',
  `Phone` VARCHAR(50) NOT NULL COMMENT '联系电话，允许为空，即可选输入',
  `Address` VARCHAR(255) NOT NULL COMMENT '地址，允许为空，即可选输入',
  `BornDate` DATETIME DEFAULT NULL COMMENT '出生时间',
  `Email` VARCHAR(50) NOT NULL COMMENT '邮箱账号，允许为空，即可选输入',
  `IdentityCard` VARCHAR(18) DEFAULT NULL COMMENT '身份证号',
  PRIMARY KEY (`StudentNo`),
  UNIQUE KEY `IdentityCard` (`IdentityCard`),
  KEY `Email` (`Email`)
) ENGINE=MYISAM DEFAULT CHARSET=utf8;

/*Data for the table `student` */

INSERT  INTO `student`(`StudentNo`,`LoginPwd`,`StudentName`,`Sex`,`GradeId`,`Phone`,`Address`,`BornDate`,`Email`,`IdentityCard`) VALUES (1000,'111111','郭靖',1,1,'13500000001','北京海淀区中关村大街1号','1986-12-11 00:00:00','test1@bdqn.cn','450323198612111234'),(1001,'123456','李文才',1,2,'13500000002','河南洛阳','1981-12-31 00:00:00','test1@bdqn.cn','450323198112311234'),(1002,'111111','李斯文',1,1,'13500000003','天津市和平区','1986-11-30 00:00:00','test1@bdqn.cn','450323198611301234'),(1003,'123456','武松',1,3,'13500000004','上海卢湾区','1986-12-31 00:00:00','test1@bdqn.cn','450323198612314234'),(1004,'123456','张三',1,4,'13500000005','北京市通州','1989-12-31 00:00:00','test1@bdqn.cn','450323198612311244'),(1005,'123456','张秋丽 ',2,1,'13500000006','广西桂林市灵川','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311214'),(1006,'123456','肖梅',2,4,'13500000007','地址不详','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311134'),(1007,'111111','欧阳峻峰',1,1,'13500000008','北京东城区','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311133'),(1008,'111111','梅超风',1,1,'13500000009','河南洛阳','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311221'),(1009,'123456','刘毅',1,2,'13500000011','安徽','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311231'),(1010,'111111','大凡',1,1,'13500000012','河南洛阳','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311044'),(1011,'111111','奥丹斯',1,1,'13500000013','北京海淀区中关村大街*号','1984-12-31 00:00:00','test1@bdqn.cn','450323198412311234'),(1012,'123456','多伦',2,3,'13500000014','广西南宁中央大街','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311334'),(1013,'123456','李梅',2,1,'13500000015','上海卢湾区','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311534'),(1014,'123456','张得',2,4,'13500000016','北京海淀区中关村大街*号','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311264'),(1015,'123456','李东方',1,4,'13500000017','广西桂林市灵川','1976-12-31 00:00:00','test1@bdqn.cn','450323197612311234'),(1016,'111111','刘奋斗',1,1,'13500000018','上海卢湾区','1986-12-31 00:00:00','test1@bdqn.cn','450323198612311251'),(1017,'123456','可可',2,3,'13500000019','北京长安街1号','1981-09-10 00:00:00','test1@bdqn.cn','450323198109108311'),(10066,'','Tom',1,1,'13500000000','','0000-00-00 00:00:00','email@22.com','33123123123123123');

/*Table structure for table `subject` */

DROP TABLE IF EXISTS `subject`;

CREATE TABLE `subject` (
  `SubjectNo` INT(11) NOT NULL AUTO_INCREMENT COMMENT '课程编号',
  `SubjectName` VARCHAR(50) DEFAULT NULL COMMENT '课程名称',
  `ClassHour` INT(4) DEFAULT NULL COMMENT '学时',
  `GradeID` INT(4) DEFAULT NULL COMMENT '年级编号',
  PRIMARY KEY (`SubjectNo`)
) ENGINE=INNODB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8;

/*Data for the table `subject` */

INSERT  INTO `subject`(`SubjectNo`,`SubjectName`,`ClassHour`,`GradeID`) VALUES (1,'高等数学-1',110,1),(2,'高等数学-2',110,2),(3,'高等数学-3',100,3),(4,'高等数学-4',130,4),(5,'C语言-1',110,1),(6,'C语言-2',110,2),(7,'C语言-3',100,3),(8,'C语言-4',130,4),(9,'JAVA第一学年',110,1),(10,'JAVA第二学年',110,2),(11,'JAVA第三学年',100,3),(12,'JAVA第四学年',130,4),(13,'数据库结构-1',110,1),(14,'数据库结构-2',110,2),(15,'数据库结构-3',100,3),(16,'数据库结构-4',130,4),(17,'C#基础',130,1);

/*!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 */;

2. 指定查询字段

  • 查询表结果时 , 可指定查询结果的数据列

    • 如 : SELECT * FROM student;

    • # 查询所有学生信息
SELECT * FROM student;

# 查询指定列(学号 , 姓名)
SELECT studentno,studentname FROM student;

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21



      ### 3. AS起别名

       AS子句作用 :

      - 可给**数据列**取一个新别名
      - 可给**表**取一个新别名
      - 可把经计算或总结的结果用另一个新名称来代替

      ```mysql
      # 这里是为列取别名(当然as关键词可以省略)
      SELECT studentno AS 学号,studentname AS 姓名 FROM student;

      # 使用as也可以为表取别名
      SELECT studentno AS 学号,studentname AS 姓名 FROM student AS s;

      # 使用as,为查询结果取一个新名字
      # CONCAT()函数拼接字符串
      SELECT CONCAT('姓名:',studentname) AS 新姓名 FROM student;

4. 去重

  • 作用 : 去掉SELECT查询返回的记录结果中重复的记录(返回所有列的值都相同),只返回一条
1
2
3
4
5
# 查看哪些同学参加了考试(学号)--去除重复项
SELECT * FROM result; # 查看考试成绩
SELECT studentno FROM result; # 查看哪些同学参加了考试
SELECT DISTINCT studentno FROM result;
# 了解:DISTINCT 去除重复项 , (默认是ALL)

5. 使用表达式的列

数据库中的表达式：文本值,列，NULL，计算表达式，变量

select 表达式 from 表

应用场景：

  • select 语句返回结果列中使用
  • select 与剧中的order by, having 等子句中使用
  • DML语句中where条件语句中使用表达式
1
2
3
4
5
6
7
# selcet查询中可以使用表达式
SELECT @@auto_increment_increment; # 查询自增步长
SELECT VERSION(); #查询版本号
SELECT 100*3-1 AS 计算结果; # 表达式

# 学员考试成绩集体提分一分查看
SELECT studentno,StudentResult+1 AS '提分后' FROM result;

6. where条件字句

  • 作用：检索数据中符合条件的值
  • 搜索条件可由一个或多个逻辑表达式组成 , 结果一般为真或假.

逻辑运算符

运算符 语法 描述
and && a and b 逻辑与
or || a or b 逻辑或
Not ! not a ! a 逻辑非 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
# 满足条件的查询(where)
SELECT Studentno,StudentResult FROM result;

# 查询考试成绩在95-100之间的
SELECT Studentno,StudentResult 
FROM result
WHERE StudentResult>=95 AND StudentResult<=100;
# AND也可以写成 &&
SELECT Studentno,StudentResult 
FROM result
WHERE StudentResult>=95 && StudentResult<=100;

# 模糊查询(对应的词:精确查询)
SELECT Studentno,StudentResult 
FROM result
WHERE StudentResult BETWEEN 95 AND 100;
# 除了1000号同学,要其他同学的成绩
SELECT studentno,studentresult
FROM result
WHERE studentno!=1000;

# 使用NOT
SELECT studentno,studentresult
FROM result
WHERE NOT studentno=1000;

7. 模糊查询

比较运算符

运算符 语法 描述
Is NUll a is null 如果操作符是null ,结果为真
Is not NUll a is not null 如果操作符不为null,结果为真
Between a between b and c 如果a在b和c之间，结果为真
Like a like b SQL匹配，如果a 匹配到 b，则结果为真
in a in (a1,a2,a3) 如果a在a1,a2,a3中，结果为真

通配符

1
2
%     --代表0到任意个字符
_     --代表1个字符

示例：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
#模糊查询 between and \ like \ in \ null

#=============================================
# LIKE
#=============================================
#查询姓李的同学的学号及姓名
#like结合使用的通配符 : % (代表0到任意个字符)  _ (一个字符)
SELECT studentno,studentname FROM student
WHERE studentname LIKE '李%';

#查询姓李的同学,后面只有一个字的
SELECT studentno,studentname FROM student
WHERE studentname LIKE '李_';

#查询姓李的同学,后面只有两个字的
SELECT studentno,studentname FROM student
WHERE studentname LIKE '李__';

#查询姓名中含有 文 字的
SELECT studentno,studentname FROM student
WHERE studentname LIKE '%文%';

#查询姓名中含有特殊字符的需要使用转义符号 '\'
#自定义转义符关键字:  ESCAPE ':'

#=============================================
# IN
#=============================================
#查询学号为1000,1001,1002的学生姓名
SELECT studentno,studentname FROM student
WHERE studentno IN (1000,1001,1002);

#查询地址在北京,南京,河南洛阳的学生
SELECT studentno,studentname,address FROM student
WHERE address IN ('北京','南京','河南洛阳');

#=============================================
# NULL 空
#=============================================
#查询出生日期没有填写的同学
#不能直接写=NULL , 这是代表错误的 , 用 is null 
SELECT studentname FROM student
WHERE BornDate IS NULL;

#查询出生日期填写的同学
SELECT studentname FROM student
WHERE BornDate IS NOT NULL;

#查询没有写家庭住址的同学(空字符串不等于null)
SELECT studentname FROM student
WHERE Address='' OR Address IS NULL;

8. 联表查询

操作 描述
Inner join 如果表中有一个匹配的值，就返回
left join 会从左表中返回所有的值，哪怕右表中没有配置的值
right join 会从右表中返回所有的值，哪怕左表中没有匹配的值
  • join on — 连接查询
  • where — 等值查询
1
2
3
4
5
6
7
8
9
10
11
12
13
/*
1. 连接查询
    如需要多张数据表的数据进行查询,则可通过连接运算符实现多个查询
内连接 inner join
    查询两个表中的结果集中的交集
外连接 outer join
    左外连接 left join
        (以左表作为基准,右边表来一一匹配,匹配不上的,返回左表的记录,右表以NULL填充)
    右外连接 right join
        (以右表作为基准,左边表来一一匹配,匹配不上的,返回右表的记录,左表以NULL填充)
        
2. 等值连接和非等值连接
*/

练习：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
#查询参加了考试的同学信息(学号,学生姓名,科目编号,分数)
SELECT * FROM student;
SELECT * FROM result;

/*思路:
(1):分析需求,确定查询的列来源于两个类,student  result,连接查询
(2):确定使用哪种连接查询?(内连接)
*/
SELECT s.studentno,studentname,subjectno,StudentResult
FROM student s
INNER JOIN result r
ON r.studentno = s.studentno

# 右连接(也可实现)
SELECT s.studentno,studentname,subjectno,StudentResult
FROM student s
RIGHT JOIN result r
ON r.studentno = s.studentno

# 等值连接
SELECT s.studentno,studentname,subjectno,StudentResult
FROM student s , result r
WHERE r.studentno = s.studentno

# 左连接 (查询了所有同学,不考试的也会查出来)
SELECT s.studentno,studentname,subjectno,StudentResult
FROM student s
LEFT JOIN result r
ON r.studentno = s.studentno

#查一下缺考的同学(左连接应用场景)
SELECT s.studentno,studentname,subjectno,StudentResult
FROM student s
LEFT JOIN result r
ON r.studentno = s.studentno
WHERE StudentResult IS NULL

#思考题:查询参加了考试的同学信息(学号,学生姓名,科目名,分数)
SELECT s.studentno,studentname,subjectname,StudentResult
FROM student s
INNER JOIN result r
ON r.studentno = s.studentno
INNER JOIN `subject` sub
ON sub.subjectno = r.subjectno

9. 自连接

准备环境

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
# 创建一个表
CREATE TABLE `category` (
  `categoryid` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主题id',
  `pid` INT(10) NOT NULL COMMENT '父id',
  `categoryName` VARCHAR(50) NOT NULL COMMENT '主题名字',
  PRIMARY KEY (`categoryid`)
) ENGINE=INNODB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8

# 插入数据
INSERT INTO `category` (`categoryid`, `pid`, `categoryName`) 
VALUES('2','1','信息技术'),
('3','1','软件开发'),
('4','3','数据库'),
('5','1','美术设计'),
('6','3','web开发'),
('7','5','ps技术'),
('8','2','办公信息');

练习：核心思想:把一张表看成两张一模一样的表,然后将这两张表连接查询(自连接)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
# 编写SQL语句,将栏目的父子关系呈现出来 (父栏目名称,子栏目名称)
# 核心思想:把一张表看成两张一模一样的表,然后将这两张表连接查询(自连接)

/*
自连接
    数据表与自身进行连接

需求:从一个包含栏目ID , 栏目名称和父栏目ID的表中 
     查询父栏目名称和其他子栏目名称
*/

SELECT a.categoryName AS '父栏目',b.categoryName AS '子栏目'
FROM category AS a,category AS b
WHERE a.`categoryid`=b.`pid`

10.分页和排序

排序 (order by)

  • 升序 ASC
  • 降序 DESC

语法：order by

  • 用于根据指定的列对结果集进行排序
  • 默认按照ASC升序对记录进行排序

练习：

1
2
3
4
5
6
7
8
9
10
# 查询 数据库结构-1 的所有考试结果(学号 学生姓名 科目名称 成绩)
# 按成绩降序排序
SELECT s.studentno,studentname,subjectname,StudentResult
FROM student s
INNER JOIN result r
ON r.studentno = s.studentno
INNER JOIN `subject` sub
ON r.subjectno = sub.subjectno
WHERE subjectname='数据库结构-1'
ORDER BY StudentResult DESC , studentno

分页（limit）

1
2
3
4
5
6
7
推导: 
    第一页 : limit 0,5
    第二页 : limit 5,5
    第三页 : limit 10,5
    ......
    第N页 : limit (pageNo-1)*pageSzie,pageSzie
    [pageNo:页码,pageSize:单页面显示条数]

练习：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
# 每页显示5条数据
SELECT s.studentno,studentname,subjectname,StudentResult
FROM student s
INNER JOIN result r
ON r.studentno = s.studentno
INNER JOIN `subject` sub
ON r.subjectno = sub.subjectno
WHERE subjectname='数据库结构-1'
ORDER BY StudentResult DESC , studentno
LIMIT 0,5

#查询 JAVA第一学年 课程成绩前10名并且分数大于80的学生信息(学号,姓名,课程名,分数)
SELECT s.studentno,studentname,subjectname,StudentResult
FROM student s
INNER JOIN result r
ON r.studentno = s.studentno
INNER JOIN `subject` sub
ON r.subjectno = sub.subjectno
WHERE subjectname='JAVA第一学年'
ORDER BY StudentResult DESC
LIMIT 0,10

11. 子查询和嵌套查询

练习：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
# 查询 数据库结构-1 的所有考试结果(学号,科目编号,成绩),并且成绩降序排列
#方法一:使用连接查询
SELECT studentno,r.subjectno,StudentResult
FROM result r 
INNER JOIN `subject` sub
ON r.`SubjectNo`=sub.`SubjectNo`
WHERE subjectname = '数据库结构-1'
ORDER BY studentresult DESC;

#方法二:使用子查询(执行顺序:由里及外)
SELECT studentno,subjectno,StudentResult
FROM result
WHERE subjectno=(
    SELECT subjectno FROM `subject` 
    WHERE subjectname = '数据库结构-1'
)
ORDER BY studentresult DESC;

#方法二:使用连接查询+子查询
#分数不小于80分的学生的学号和姓名
SELECT r.studentno,studentname FROM student s
INNER JOIN result r ON s.`StudentNo`=r.`StudentNo`
WHERE StudentResult>=80

#在上面SQL基础上,添加需求:课程为 高等数学-2
SELECT r.studentno,studentname FROM student s
INNER JOIN result r ON s.`StudentNo`=r.`StudentNo`
WHERE StudentResult>=80 AND subjectno=(
    SELECT subjectno FROM `subject`
    WHERE subjectname = '高等数学-2'
)

#方法三:使用子查询
#分步写简单sql语句,然后将其嵌套起来
SELECT studentno,studentname FROM student WHERE studentno IN(
    SELECT studentno FROM result WHERE StudentResult>=80 AND subjectno=(
        SELECT subjectno FROM `subject` WHERE subjectname = '高等数学-2'
    )
)

12. 分组查询

语法：group by

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
# 查询不同课程的平均分,最高分,最低分
# 前提:根据不同的课程进行分组

SELECT subjectname,AVG(studentresult) AS 平均分,MAX(StudentResult) AS 最高分,MIN(StudentResult) AS 最低分
FROM result AS r
INNER JOIN `subject` AS s
ON r.subjectno = s.subjectno
GROUP BY r.subjectno
HAVING 平均分>80;

/*
where写在group by前面.
要是放在分组后面的筛选
要使用HAVING..
*/
打赏
  • 版权声明： 本博客所有文章除特别声明外，均采用 Apache License 2.0 许可协议。转载请注明出处！
  • © 2019-2022 Zhuuu
  • PV: UV:

请我喝杯咖啡吧~

支付宝
微信