数据库SQL实战练习6

1、存在actor表，包含如下列信息：

CREATE TABLE IF NOT EXISTS actor (
actor_id smallint(5) NOT NULL PRIMARY KEY,
first_name varchar(45) NOT NULL,
last_name varchar(45) NOT NULL,
last_update timestamp NOT NULL DEFAULT (datetime(‘now’,‘localtime’)));
现在在last_update后面新增加一列名字为create_date, 类型为datetime, NOT NULL，默认值为’0000 00:00:00’

alter table actor add column create_date datetime not null default '0000-00-00 00:00:00';

2、构造一个触发器audit_log，在向employees_test表中插入一条数据的时候，触发插入相关的数据到audit中。

CREATE TABLE employees_test(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);
CREATE TABLE audit(
EMP_no INT NOT NULL,
NAME TEXT NOT NULL
);

create trigger audit_log
after  insert on employees_test
for each row 
begin
insert into audit values (new.id,new.name);
end;
-- 插入的时候只有new，更新的话还有old

3、删除emp_no重复的记录，只保留最小的id对应的记录。

CREATE TABLE IF NOT EXISTS titles_test (
id int(11) not null primary key,
emp_no int(11) NOT NULL,
title varchar(50) NOT NULL,
from_date date NOT NULL,
to_date date DEFAULT NULL);

insert into titles_test values (‘1’, ‘10001’, ‘Senior Engineer’, ‘1986-06-26’, ‘9999-01-01’),
(‘2’, ‘10002’, ‘Staff’, ‘1996-08-03’, ‘9999-01-01’),
(‘3’, ‘10003’, ‘Senior Engineer’, ‘1995-12-03’, ‘9999-01-01’),
(‘4’, ‘10004’, ‘Senior Engineer’, ‘1995-12-03’, ‘9999-01-01’),
(‘5’, ‘10001’, ‘Senior Engineer’, ‘1986-06-26’, ‘9999-01-01’),
(‘6’, ‘10002’, ‘Staff’, ‘1996-08-03’, ‘9999-01-01’),
(‘7’, ‘10003’, ‘Senior Engineer’, ‘1995-12-03’, ‘9999-01-01’);

delete from  titles_test  where id in (select max(id) from titles_test group by emp_no having count(emp_no) >= 2)

4、将所有to_date为9999-01-01的全部更新为NULL,且 from_date更新为2001-01-01。

CREATE TABLE IF NOT EXISTS titles_test (
id int(11) not null primary key,
emp_no int(11) NOT NULL,
title varchar(50) NOT NULL,
from_date date NOT NULL,
to_date date DEFAULT NULL);

update titles_test 
set to_date = NULL , from_date = '2001-01-01'
where to_date = '9999-01-01'

5、将id=5以及emp_no=10001的行数据替换成id=5以及emp_no=10005,其他数据保持不变，使用replace实现。

CREATE TABLE IF NOT EXISTS titles_test (
id int(11) not null primary key,
emp_no int(11) NOT NULL,
title varchar(50) NOT NULL,
from_date date NOT NULL,
to_date date DEFAULT NULL);

-- UPDATE titles_test SET emp_no = 10005 WHERE id = 5
update titles_test  set emp_no = replace(emp_no,10001,10005) where id = 5

6、将titles_test表名修改为titles_2017。

CREATE TABLE IF NOT EXISTS titles_test (
id int(11) not null primary key,
emp_no int(11) NOT NULL,
title varchar(50) NOT NULL,
from_date date NOT NULL,
to_date date DEFAULT NULL);

alter table titles_test rename to titles_2017

7、在audit表上创建外键约束，其emp_no对应employees_test表的主键id。

CREATE TABLE employees_test(
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR(50),
SALARY REAL
);

CREATE TABLE audit(
EMP_no INT NOT NULL,
create_date datetime NOT NULL
);

-- 先drop table ，再创建带有外键约束的table。
/*DROP TABLE audit;
CREATE TABLE audit(
    EMP_no INT NOT NULL,
    create_date datetime NOT NULL,
    FOREIGN KEY (EMP_no) REFERENCES employees_test(ID));*/

/*
DROP TABLE audit;
CREATE TABLE audit(
    EMP_no INT NOT NULL,
    create_date datetime NOT NULL,
    FOREIGN KEY(EMP_no) REFERENCES employees_test(ID));*/


drop table audit;
CREATE TABLE audit(
    EMP_no INT NOT NULL,
    create_date datetime NOT NULL,
    foreign key(EMP_no) references employees_test(ID));

8、将所有获取奖金的员工当前的薪水增加10%。

create table emp_bonus(
emp_no int not null,
recevied datetime not null,
btype smallint not null);
CREATE TABLE salaries (
emp_no int(11) NOT NULL,
salary int(11) NOT NULL,
from_date date NOT NULL,
to_date date NOT NULL, PRIMARY KEY (emp_no,from_date));

update  salaries  set salary = salary * 1.1 where emp_no in (select emp_bonus.emp_no
                                                             from emp_bonus ,  salaries
                                                             where emp_bonus.emp_no =salaries.emp_no)

9、查找字符串’10,A,B’ 中逗号’,'出现的次数cnt。

select length('10,A,B') - length(replace('10,A,B',",","")) cnt;

10、分页查询employees表，每5行一页，返回第2页的数据

CREATE TABLE employees (
emp_no int(11) NOT NULL,
birth_date date NOT NULL,
first_name varchar(14) NOT NULL,
last_name varchar(16) NOT NULL,
gender char(1) NOT NULL,
hire_date date NOT NULL,
PRIMARY KEY (emp_no));

-- 6 -10 行记录 0,1从第一行开始 返回一条记录 / 2,4第3行开始返回 返回4行记录
-- (pageNo - 1)pageNum - pageNum
select *
from employees
limit 5,5

11、查找排除当前最大、最小salary之后的员工的平均工资avg_salary。

CREATE TABLE salaries ( emp_no int(11) NOT NULL,
salary int(11) NOT NULL,
from_date date NOT NULL,
to_date date NOT NULL,
PRIMARY KEY (emp_no,from_date));
输出格式:
avg_salary
69462.5555555556

select avg(salary)
from salaries
where to_date = '9999-01-01'
and salary <> (select max(salary) from salaries)
and salary <> (select min(salary) from salaries)

如有书写错误或其他答案，欢迎交流，谢谢观看！