Week13 Lec1 SQL

8/8/2019 Week13 Lec1 SQL

1/18

SQL

Summarizing underlying rows:Select s.ssn, s.lname, count(r.lname)

from em lo ee s em lo ee r

where s.ssn=r.superssn

group y s.ssn, s. name;

s.ssn s.lname r.lname

333445555 Wong 3

987654321 Wallace 2

1


2/18

SQL

Eliminating Groups from the result:Select s.ssn, s.lname, count(r.lname)

from em lo ee s em lo ee r

where s.ssn=r.superssn

group y s.ssn, s. name

having count(r.lname) < 3;

s.ssn s.lname count(r.lname)

888665555 Borg 2

987654321 Wallace 2

2


3/18

SQL

Special joins:

Outer join table

this example is a right outer join - lists every department

regardless of whether or not it has a manager

SELECT department.dnumber, department.dname,

employee.fname, employee.lnameFROM

employee RIGHT OUTER JOIN department

=. .

3


4/18

SQL

Special joins:

Inner join table

this example is an inner join - lists employees and their

departments

. , . , . ,

employee.lname

FROM

de artment INNER JOIN em loyee

ON department.dnumber = employee.dno;

SELECT department.dnumber, department.dname, employee.fname,

employee.lnameFROM department, employee

WHERE department.dnumber = employee.dno;

4


5/18

SQL

Special joins:

Inner join table with a Where clause


departments, but only for the Research department


employee.fname, employee.lnameFROM

department INNER JOIN employee

=. .

WHERE dname = 'Research';

5


6/18

SQL

Special joins:

Inner join table with a Where clause


departments, but only for the Research department


employee.fname, employee.lnameFROM department, employee

WHERE department.dnumber = employee.dno and

= ' '

6


7/18

SQL

Special joins:

Inner joins and a Where clause

this example lists employees working on a project that is

not where their department is located

SELECT employee.fname, employee.lname, works_on.pno, project.plocation

FROMpro ec

(employee INNER JOIN works_on ON employee.ssn = works_on.essn)

ON project.pnumber = works_on.pno

plocation not in (select dlocation from dept_locations where dnumber = dno);

7


8/18

SQL

Comparison:

SELECT employee.ssn, employee.fname, employee.lname,

project.pnumber, project.plocation

FROM em lo ee ro ect works on _

WHERE

employee.ssn = works_on.essn and. = _ .

plocation NOT IN

(SELECT dlocation FROM dept_locations WHERE

dnumber=employee.dno);

8


9/18

SQL

.

Insert

DeleteINSERT INTO employee ( fname, lname, ssn, dno )

VALUES ( "Joe", "Smith", 909, 1);

' '_ , , .

Create table depts_info (dept_name varchar(15), no_o_emp

n eger, o a _sa ec ma ,

Insert into depts_info select dname, count(*), sum(salary)

9

from department d, employee e where d.dnumber=e.dno

group by dname


10/18

SQL

Insert

DeleteUPDATE employee SET salary = 100000

WHERE ssn=909;

Set salary = salary*1.1

Where dno in ( select dnumber

rom epar men w ere name= esearc

DELETE FROM employee WHERE ssn=909;

10


11/18

SQL

Views:

Use a Create View command

essentially a select specifying the data that makes up the view

,

CREATE VIEW Enames lname fname

AS SELECT LNAME, FNAME

FROM EMPLOYEE

11


12/18

SQL

CREATE VIEW DEPT_INFO (DEPT_NAME,

NO_OF_EMPS,

TOTAL_SAL)

AS SELECT DNAME, COUNT(*), SUM(SALARY)

FROM DEPARTMENT EMPLOYEE

WHERE DNUMBER = DNO

GROUP BY DNAME;

12


13/18

SQL

Views are very common in business systems

users view of data is simplified

reate ew mp ro as se ect name, name, pno rom

employee inner join .

a form of securit - user sees onl the data he/she needs to

As complex as needed

if the primary key is preserved, updates to a base table through a

view is possible

13


14/18

SQL

Assertions can be used for some constraints

e.g. rea e sser on ... ... Executed andenforced by DBMS

Constraint: The salary of an employee must not be greater than

the salary of the manager of the department that the employee

works for.

CREATE ASSERTION salary_constraint

* ,employee m, department d

where e.salary > m.salary and e.dno=d.dnumber and

14

d.mgrssn=m.ssn));


15/18

SQL

ssert ons n o vers on o

Assert

trigger

Assert statementAssert SALARY_Constraint on employee e,

,

not (e.salary > m.salary and e.dno=d.dnumber and

d.mgrssn=m.ssn);Trigger

DEFINE trigger SALARY_TRIGGER on

em lo ee e em lo ee m de artment d:

(e.salary > m.salary and e.dno=d.dnumber and

d.mgrssn=m.ssn

15

_ _ .


16/18

SQL

CREATE TABLE T4 (a INTEGER, b CHAR(10));

c , ;

CREATE TRIGGER trig1

AFTER INSERT ON T4

FOR EACH ROW WHEN (newRow.a


17/18

SQL

Security: Grant and Revoke are used to specify user privileges

Grant select, update on Employee to Diane;

_

Embedded SQL: SQL can be placed within 3GL programs

ransac ons: sys ems mp emen e proper es

17


18/18

SQL

Exercises 8.18 to 8.20 and 8.24

Homework

18

Week13 Lec1 SQL

Documents

Transcript of Week13 Lec1 SQL