MySql的sql語法練習【員工、部門】

本文轉載自查看原文 2019-01-25 10:10 791

一、dept和emp表結構：

create table dept
(
deptno int(100) not null,
dname varchar(255),
loc varchar(255),
);
alter table dept add constraint PK_DEPT primary key (deptno);

create table emp
(
empno int(100) not null,
ename   varchar(255),
job varchar(255),,
mgr int(100),
hiredate date,
sal int(100),
comm   int(100),
deptno   int(100)
);
alter table EMP add constraint PK_EMP primary key (empno);

二、初始化數據：

insert into DEPT (DEPTNO, DNAME, LOC)
values (10, 'ACCOUNTING', 'NEW YORK');
insert into DEPT (DEPTNO, DNAME, LOC)
values (20, 'RESEARCH', 'DALLAS');
insert into DEPT (DEPTNO, DNAME, LOC)
values (30, 'SALES', 'CHICAGO');
insert into DEPT (DEPTNO, DNAME, LOC)
values (40, 'OPERATIONS', 'BOSTON');
commit;

insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7369, 'SMITH', 'CLERK', 7902, str_to_date('1980-12-17', '%Y-%m-%d'), 800, null, 20);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7499, 'ALLEN', 'SALESMAN', 7698, str_to_date('1981-02-20', '%Y-%m-%d'), 1600, 300, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7521, 'WARD', 'SALESMAN', 7698, str_to_date('1981-02-22', '%Y-%m-%d'), 1250, 500, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7566, 'JONES', 'MANAGER', 7839, str_to_date('1981-04-02', '%Y-%m-%d'), 2975, null, 20);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7654, 'MARTIN', 'SALESMAN', 7698, str_to_date('1981-09-28', '%Y-%m-%d'), 1250, 1400, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7698, 'BLAKE', 'MANAGER', 7839, str_to_date('1981-05-01', '%Y-%m-%d'), 2850, null, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7782, 'CLARK', 'MANAGER', 7839, str_to_date('1981-06-09', '%Y-%m-%d'), 2450, null, 10);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7788, 'SCOTT', 'ANALYST', 7566, str_to_date('1987-04-19', '%Y-%m-%d'), 3000, null, 20);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7839, 'KING', 'PRESIDENT', null, str_to_date('1981-11-17', '%Y-%m-%d'), 5000, null, 10);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7844, 'TURNER', 'SALESMAN', 7698, str_to_date('1981-09-08', '%Y-%m-%d'), 1500, 0, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7876, 'ADAMS', 'CLERK', 7788, str_to_date('1987-05-23', '%Y-%m-%d'), 1100, null, 20);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7900, 'JAMES', 'CLERK', 7698, str_to_date('1981-12-03', '%Y-%m-%d'), 950, null, 30);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7902, 'FORD', 'ANALYST', 7566, str_to_date('1981-12-03', '%Y-%m-%d'), 3000, null, 20);
insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7934, 'MILLER', 'CLERK', 7782, str_to_date('1982-01-23', '%Y-%m-%d'), 1300, null, 10);

insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7978, 'MILLER', 'CLERK', 7782, str_to_date('1982-01-23', '%Y-%m-%d'), 1300, null, 40);

insert into EMP (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO)
values (7972, 'MIKER', 'CLERK', 7792, str_to_date('1982-07-23', '%Y-%m-%d'), 3300, null, 40);

commit;

三、題目練習

1．列出至少有三個員工的所有部門。

select deptno from emp group by deptno having count(*)>3;

解析：該語句主要學習分組函數group by，以及對分組后過濾的條件函數having。需要注意的是使用了分組函數語句的select字段中不能包含group by后沒有的字段，原因是如果顯示非分組的字段就可能顯示多條記錄，就達不到按某字段分組的目的。Having只能用在分組函數group by后，相當於對分組后的記錄做where條件過濾。