目录
目录:
一.视图
1.介绍什么是视图
2.视图的语法
语法讲解
实例操作
二.MySQL面试题
1.SQL脚本
2.面试题实战
三.思维导图
目录:
随着数字化时代的飞速发展,数据库技术,特别是MySQL,已经成为IT领域中不可或缺的一环。从简单的数据存储到复杂的数据分析,从个人博客到大型企业的核心系统,MySQL都在背后默默地发挥着作用。而在这不断演变的过程中,我们对于MySQL的了解和掌握也需要与时俱进。
在之前的博客中,我们已经探讨了MySQL的许多基础和进阶功能。但今天,我们要深入到一个经常被忽视,但又非常重要的主题——视图(View)。视图在数据库中起到了一个非常特殊的角色,它能够简化复杂的查询操作,提高数据的安全性,并帮助我们更好地组织和理解数据。
此外,为了更好地服务我们的读者,这篇博客还将涉及到一些常见的MySQL面试题。通过解答这些问题,我们不仅能够测试和巩固自己的知识,还能为即将参加面试的朋友们提供一些参考和启示。
在接下来的篇幅中,我们将深入探讨视图的创建、使用和优化,以及解答那些常常在面试中出现的关于MySQL的疑问。希望通过这次的学习,你能对MySQL有更深入的理解和掌握。
准备好了吗?让我们开始这次的探索之旅!
一.视图
1.介绍什么是视图
虚拟表,和普通表一样使用
2.视图的语法
语法讲解
创建视图
create view 视图名 as 查询语句 ;
视图修改
#方式一
create or replace view 视图名
as
查询语句;
#方式二
alert view 视图名
as
查询语句;
删除视图
drop view 视图名
查看视图
#查看视图相关字段
desc 视图名;
#查看视图相关语句
show create view 视图名;
实例操作
创建视图
CREATE VIEW v_su as
SELECT s.*,sc.cid,sc.score
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid;
修改视图
ALTER VIEW v_su as
SELECT s.*,sc.cid,sc.score
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid
CREATE or REPLACE VIEW v_zx as
SELECT s.*,sc.cid,sc.score
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid;
查看视图
desc v_sU
SHOW CREATE view v_su
二.MySQL面试题
1.SQL脚本
/*
Navicat Premium Data Transfer
Source Server : localhost
Source Server Type : MySQL
Source Server Version : 80018
Source Host : localhost:3306
Source Schema : mybatis_ssm
Target Server Type : MySQL
Target Server Version : 80018
File Encoding : 65001
Date: 04/07/2023 23:53:33
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for t_mysql_course
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_course`;
CREATE TABLE `t_mysql_course` (
`cid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程编号',
`cname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程名称',
`tid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师编号',
PRIMARY KEY (`cid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '课程信息表' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of t_mysql_course
-- ----------------------------
INSERT INTO `t_mysql_course` VALUES ('01', '语文', '02');
INSERT INTO `t_mysql_course` VALUES ('02', '数学', '01');
INSERT INTO `t_mysql_course` VALUES ('03', '英语', '03');
-- ----------------------------
-- Table structure for t_mysql_score
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_score`;
CREATE TABLE `t_mysql_score` (
`sid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生编号,外键',
`cid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '课程编号,外键',
`score` float NULL DEFAULT 0 COMMENT '成绩',
INDEX `sid`(`sid`) USING BTREE,
INDEX `cid`(`cid`) USING BTREE,
CONSTRAINT `t_mysql_score_ibfk_1` FOREIGN KEY (`sid`) REFERENCES `t_mysql_student` (`sid`) ON DELETE RESTRICT ON UPDATE RESTRICT,
CONSTRAINT `t_mysql_score_ibfk_2` FOREIGN KEY (`cid`) REFERENCES `t_mysql_course` (`cid`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '成绩信息表' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of t_mysql_score
-- ----------------------------
INSERT INTO `t_mysql_score` VALUES ('01', '01', 80);
INSERT INTO `t_mysql_score` VALUES ('01', '02', 90);
INSERT INTO `t_mysql_score` VALUES ('01', '03', 99);
INSERT INTO `t_mysql_score` VALUES ('02', '01', 70);
INSERT INTO `t_mysql_score` VALUES ('02', '02', 60);
INSERT INTO `t_mysql_score` VALUES ('02', '03', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '01', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '02', 80);
INSERT INTO `t_mysql_score` VALUES ('03', '03', 80);
INSERT INTO `t_mysql_score` VALUES ('04', '01', 50);
INSERT INTO `t_mysql_score` VALUES ('04', '02', 30);
INSERT INTO `t_mysql_score` VALUES ('04', '03', 20);
INSERT INTO `t_mysql_score` VALUES ('05', '01', 76);
INSERT INTO `t_mysql_score` VALUES ('05', '02', 87);
INSERT INTO `t_mysql_score` VALUES ('06', '01', 31);
INSERT INTO `t_mysql_score` VALUES ('06', '03', 34);
INSERT INTO `t_mysql_score` VALUES ('07', '02', 89);
INSERT INTO `t_mysql_score` VALUES ('07', '03', 98);
-- ----------------------------
-- Table structure for t_mysql_student
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_student`;
CREATE TABLE `t_mysql_student` (
`sid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生编号',
`sname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生名称',
`sage` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生年龄',
`ssex` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '学生性别',
PRIMARY KEY (`sid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '学生信息表' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of t_mysql_student
-- ----------------------------
INSERT INTO `t_mysql_student` VALUES ('01', '赵雷', '1990-01-01', '男');
INSERT INTO `t_mysql_student` VALUES ('02', '钱电', '1990-12-21', '男');
INSERT INTO `t_mysql_student` VALUES ('03', '孙风', '1990-12-20', '男');
INSERT INTO `t_mysql_student` VALUES ('04', '李云', '1990-12-06', '男');
INSERT INTO `t_mysql_student` VALUES ('05', '周梅', '1991-12-01', '女');
INSERT INTO `t_mysql_student` VALUES ('06', '吴兰', '1992-01-01', '女');
INSERT INTO `t_mysql_student` VALUES ('07', '郑竹', '1989-01-01', '女');
INSERT INTO `t_mysql_student` VALUES ('09', '张三', '2017-12-20', '女');
INSERT INTO `t_mysql_student` VALUES ('10', '李四', '2017-12-25', '女');
INSERT INTO `t_mysql_student` VALUES ('11', '李四', '2012-06-06', '女');
INSERT INTO `t_mysql_student` VALUES ('12', '赵六', '2013-06-13', '女');
INSERT INTO `t_mysql_student` VALUES ('13', '孙七', '2014-06-01', '女');
-- ----------------------------
-- Table structure for t_mysql_teacher
-- ----------------------------
DROP TABLE IF EXISTS `t_mysql_teacher`;
CREATE TABLE `t_mysql_teacher` (
`tid` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师编号',
`tname` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT '教师名称',
PRIMARY KEY (`tid`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '教师信息表' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of t_mysql_teacher
-- ----------------------------
INSERT INTO `t_mysql_teacher` VALUES ('01', '张三');
INSERT INTO `t_mysql_teacher` VALUES ('02', '李四');
INSERT INTO `t_mysql_teacher` VALUES ('03', '王五');
SET FOREIGN_KEY_CHECKS = 1;
2.面试题实战
1.查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数
#考察内容:联表查询 内连接 所需表:t_mysql_student t_mysql_score
SELECT
s.*,
( CASE WHEN t1.cid = '01' THEN t1.score END ) 语文,
( CASE WHEN t2.cid = '02' THEN t2.score END ) 数学
FROM
t_mysql_student s,
( SELECT * FROM t_mysql_score WHERE cid = '01' ) t1,
( SELECT * FROM t_mysql_score WHERE cid = '02' ) t2
WHERE
s.sid = t1.sid
AND t1.sid = t2.sid
AND t1.score > t2.score
2. 查询同时存在" 01 "课程和" 02 "课程的情况
SELECT
s.*,
( CASE WHEN t1.cid = '01' THEN t1.score END ) 语文,
( CASE WHEN t2.cid = '02' THEN t2.score END ) 数学
FROM
t_mysql_student s,
( SELECT * FROM t_mysql_score WHERE cid = '01' ) t1,
( SELECT * FROM t_mysql_score WHERE cid = '02' ) t2
WHERE
s.sid = t1.sid
AND t1.sid = t2.sid
03)查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
#外连接
SELECT * from
( SELECT * FROM t_mysql_score WHERE cid = '01' ) t1
LEFT JOIN
( SELECT * FROM t_mysql_score WHERE cid = '02' ) t2
on t1.sid=t2.sid
04)查询不存在" 01 "课程但存在" 02 "课程的情况
#子查询
SELECT
*
FROM
t_mysql_student s,
t_mysql_score sc
WHERE
s.sid = sc.sid
AND s.sid NOT IN ( SELECT sid FROM t_mysql_score WHERE cid = '01' )
AND sc.cid = '02'
05)查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
#聚合函数=》 分组 外连接
SELECT
s.sid,
s.sname,
ROUND( AVG( sc.score ) ) 分数
FROM
t_mysql_student s
LEFT JOIN t_mysql_score sc ON s.sid = sc.sid
GROUP BY
s.sid,
s.sname
HAVING
分数 >= 60
06)查询在t_mysql_score表存在成绩的学生信息
SELECT
s.sid,
s.sname
FROM
t_mysql_student s
INNER JOIN t_mysql_score sc ON s.sid = sc.sid
GROUP BY
s.sid,
s.sname
07)查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )
#考核点 聚合函数 外连接
SELECT
s.sid,
s.sname,
COUNT( sc.cid ),
SUM( sc.score )
FROM
t_mysql_score sc,
t_mysql_student s
WHERE
sc.sid = s.sid
GROUP BY
s.sid,
s.sname
08)查询「李」姓老师的数量
select count(*) from t_mysql_teacher where tname like '李%'
文章来源:https://www.toymoban.com/news/detail-782261.html
三.思维导图
文章来源地址https://www.toymoban.com/news/detail-782261.html
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