sql语句练习

MySQL的常见sql语句

• 1.首先选择数据库，并删除多余的表：

use lik;
drop table account, log, tb_brand;

• 2.创建表：学生表、课程表、以及每个学生选的课程表

create table student(id   int auto_increment comment '主键ID' primary key,name varchar(10) null comment '姓名',no   varchar(10) null comment '学号'
)comment '学生表';create table course(id int auto_increment comment '主键ID' primary key,name varchar(10) null comment '课程名称'
)comment '课程表';create table student_course(id int auto_increment comment '主键' primary key,studentid int not null comment '学生ID',courseid  int not null comment '课程ID',constraint fk_courseid foreign key (courseid) references course (id),constraint fk_studentid foreign key (studentid) references student (id)
)comment '学生课程中间表';

初级增删改查

• 1.增：给对应的表插入数据

#插入学生信息
INSERT INTO student (name, no) VALUES ('黛绮丝', '2000100101');
INSERT INTO student (name, no) VALUES ('谢逊', '2000100102');
INSERT INTO student (name, no) VALUES ('殷天正', '2000100103');
INSERT INTO student (name, no) VALUES ('韦一笑', '2000100104');#插入课程
INSERT INTO course (name) VALUES ('Java');
INSERT INTO course (name) VALUES ('PHP');
INSERT INTO course (name) VALUES ('MySQL');
INSERT INTO course (name) VALUES ('Hadoop');#插入学生所选课程
INSERT INTO student_course (studentid, courseid) VALUES (1, 1);
INSERT INTO student_course (studentid, courseid) VALUES (1, 2);
INSERT INTO student_course (studentid, courseid) VALUES (1, 3);
INSERT INTO student_course (studentid, courseid) VALUES (2, 2);
INSERT INTO student_course (studentid, courseid) VALUES (2, 3);
INSERT INTO student_course (studentid, courseid) VALUES (3, 4);

• 2.删：删除某个学生，以及该学生对应选的课程信息

begin; #start transaction;
delete from student  where id = 4;
delete from student_course where studentid = 4;
commit;

• 3.改：

update student set name = '张无忌' where id = 1;

• 4.查：多表联查

select brand_name, description from tb_brand where id = 1;select s.name name, c.name course from student s, course c, student_course sc where s.id = sc.studentid and c.id = sc.courseid;

进阶

大数据量情况下：

• 1.批量插入：

insert into student values (null, '赵敏', 13411555), (null, '小昭', 2344144),(null, '张三丰', 13412414);

• 2.分段式批量插入：一次插入5000~10000适当，可以分段批量插入

start transcation；
insert into student values(null, '赵敏', 13411555), (null, '小昭', 2344144),(null, '张三丰', 13412414);
insert into student values(null, '赵敏', 13411555), (null, '小昭', 2344144),(null, '张三丰', 13412414);
insert into student values(null, '赵敏', 13411555), (null, '小昭', 2344144),(null, '张三丰', 13412414);
commit;

• 3.文件导入式插入：
  一次需要插入上百万条数据时，使用insert语句插入性能较低，此时可以使用MySQL提供的load指令进行插入。

  • 1.连接MySQL服务端时，加上参数： --local-infile
mysql -- local-infile -u root -p
  • 2.设置全局参数local_infile为1，开启从本地加载文件导入数据的开关：
    set global local_infile = 1;
  • 3.执行load指定将准备好的数据文件中的数据加载到表结构中：

load data local infile '/root/sql.log' into table `student` fields terminated by ',' lines terminated by '\n';

• 其中文件的数据要与表字段顺序一致，并且中间用逗号或者空格隔开，像上面的sql语句就是表示将数据以'\n'作为换行，','作为分隔符进行读取：