mysql视图详细笔记

 1 #视图 2 /* 3 含义：虚拟表，和普通表一样使用 4 mysql5.1版本出现的新特性，是通过表动态生成的数据 5  6 比如：舞蹈班和普通班级的对比 7  创建语法的关键字 是否实际占用物理空间 使用 8  9 视图 create view  只是保存了sql逻辑 增删改查，只是一般不能增删改 10  11 表 create table  保存了数据  增删改查 12  13  14 */ 15  16 #案例：查询姓张的学生名和专业名 17 SELECT stuname,majorname 18 FROM stuinfo s 19 INNER JOIN major m ON s.`majorid`= m.`id` 20 WHERE s.`stuname` LIKE '张%'; 21  22 CREATE VIEW v1 23 AS 24 SELECT stuname,majorname 25 FROM stuinfo s 26 INNER JOIN major m ON s.`majorid`= m.`id`; 27  28 SELECT * FROM v1 WHERE stuname LIKE '张%'; 29  30  31 #一、创建视图 32 /* 33 语法： 34 create view 视图名 35 as 36 查询语句; 37  38 */ 39 USE myemployees; 40  41 #1.查询姓名中包含a字符的员工名、部门名和工种信息 42 #①创建 43 CREATE VIEW myv1 44 AS 45  46 SELECT last_name,department_name,job_title 47 FROM employees e 48 JOIN departments d ON e.department_id = d.department_id 49 JOIN jobs j ON j.job_id = e.job_id; 50  51  52 #②使用 53 SELECT * FROM myv1 WHERE last_name LIKE '%a%'; 54  55  56  57  58  59  60 #2.查询各部门的平均工资级别 61  62 #①创建视图查看每个部门的平均工资 63 CREATE VIEW myv2 64 AS 65 SELECT AVG(salary) ag,department_id 66 FROM employees 67 GROUP BY department_id; 68  69 #②使用 70 SELECT myv2.`ag`,g.grade_level 71 FROM myv2 72 JOIN job_grades g 73 ON myv2.`ag` BETWEEN g.`lowest_sal` AND g.`highest_sal`; 74  75  76  77 #3.查询平均工资最低的部门信息 78  79 SELECT * FROM myv2 ORDER BY ag LIMIT 1; 80  81 #4.查询平均工资最低的部门名和工资 82  83 CREATE VIEW myv3 84 AS 85 SELECT * FROM myv2 ORDER BY ag LIMIT 1; 86  87  88 SELECT d.*,m.ag 89 FROM myv3 m 90 JOIN departments d 91 ON m.`department_id`=d.`department_id`; 92  93  94  95  96 #二、视图的修改 97  98 #方式一： 99 /*100 create or replace view 视图名101 as102 查询语句;103 104 */105 SELECT * FROM myv3 106 107 CREATE OR REPLACE VIEW myv3108 AS109 SELECT AVG(salary),job_id110 FROM employees111 GROUP BY job_id;112 113 #方式二：114 /*115 语法：116 alter view 视图名117 as 118 查询语句;119 120 */121 ALTER VIEW myv3122 AS123 SELECT * FROM employees;124 125 #三、删除视图126 127 /*128 129 语法：drop view 视图名,视图名,...;130 */131 132 DROP VIEW emp_v1,emp_v2,myv3;133 134 135 #四、查看视图136 137 DESC myv3;138 139 SHOW CREATE VIEW myv3;140 141 142 #五、视图的更新143 144 CREATE OR REPLACE VIEW myv1145 AS146 SELECT last_name,email,salary*12*(1+IFNULL(commission_pct,0)) "annual salary"147 FROM employees;148 149 CREATE OR REPLACE VIEW myv1150 AS151 SELECT last_name,email152 FROM employees;153 154 155 SELECT * FROM myv1;156 SELECT * FROM employees;157 #1.插入158 159 INSERT INTO myv1 VALUES('张飞','zf@qq.com');160 161 #2.修改162 UPDATE myv1 SET last_name = '张无忌' WHERE last_name='张飞';163 164 #3.删除165 DELETE FROM myv1 WHERE last_name = '张无忌';166 167 #具备以下特点的视图不允许更新168 169 170 #①包含以下关键字的sql语句：分组函数、distinct、group by、having、union或者union all171 172 CREATE OR REPLACE VIEW myv1173 AS174 SELECT MAX(salary) m,department_id175 FROM employees176 GROUP BY department_id;177 178 SELECT * FROM myv1;179 180 #更新181 UPDATE myv1 SET m=9000 WHERE department_id=10;182 183 #②常量视图184 CREATE OR REPLACE VIEW myv2185 AS186 187 SELECT 'john' NAME;188 189 SELECT * FROM myv2;190 191 #更新192 UPDATE myv2 SET NAME='lucy';193 194 195 196 197 198 #③Select中包含子查询199 200 CREATE OR REPLACE VIEW myv3201 AS202 203 SELECT department_id,(SELECT MAX(salary) FROM employees) 最高工资204 FROM departments;205 206 #更新207 SELECT * FROM myv3;208 UPDATE myv3 SET 最高工资=100000;209 210 211 #④join212 CREATE OR REPLACE VIEW myv4213 AS214 215 SELECT last_name,department_name216 FROM employees e217 JOIN departments d218 ON e.department_id = d.department_id;219 220 #更新221 222 SELECT * FROM myv4;223 UPDATE myv4 SET last_name = '张飞' WHERE last_name='Whalen';224 INSERT INTO myv4 VALUES('陈真','xxxx');225 226 227 228 #⑤from一个不能更新的视图229 CREATE OR REPLACE VIEW myv5230 AS231 232 SELECT * FROM myv3;233 234 #更新235 236 SELECT * FROM myv5;237 238 UPDATE myv5 SET 最高工资=10000 WHERE department_id=60;239 240 241 242 #⑥where子句的子查询引用了from子句中的表243 244 CREATE OR REPLACE VIEW myv6245 AS246 247 SELECT last_name,email,salary248 FROM employees249 WHERE employee_id IN(250  SELECT manager_id251  FROM employees252  WHERE manager_id IS NOT NULL253 );254 255 #更新256 SELECT * FROM myv6;257 UPDATE myv6 SET salary=10000 WHERE last_name = 'k_ing';

 

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