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Introduction to SQL

Lecture 5

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Note

in different implementations the syntax might slightly differ different features might be available

in certain implementations non-relational operators might be supported certain relational operations might not be

possible to be performed

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Operations

create table restrict, project and join (via SELECT) insert, update, delete create view, query view

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CREATE TABLE

CREATE TABLE Depts (Dept_id CHAR(2),Dept_name CHAR(20),Budget DECIMAL(8),

PRIMARY KEY (Dept_id));

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CREATE TABLE

CREATE TABLE Emps (E_id CHAR(2),E_name CHAR(20),Dept_id CHAR(2),Salary DECIMAL(5),

PRIMARY KEY (E_id), FOREIGN KEY (Dept_id) REFERENCES Depts);

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restrict (via SELECT)

SELECT ( E_id, E_name, Dept_id, Salary )FROM EmpsWHERE Salary > 33000;

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project (via SELECT)

SELECT ( E_name, Salary )FROM Emps ;

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join (via SELECT)

SELECT ( Depts.Dept_id, Dept_name, Budget, E_id, E_name, Salary )

FROM Emps, DeptsWHERE Depts.Dept_id = Emps.Dept_id ;

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restrict, project and join (via SELECT)

SELECT ( Dept_name, E_name, Salary )FROM Emps, DeptsWHERE Depts.Dept_id = Emps.Dept_id AND Salary > 33000;

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INSERT single row

INSERTINTO Emps ( E_id, E_name, Dept_id, Salary )VALUES ( ‘E1’, ‘Smith’, ‘D1’, 40000 ) ;

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INSERT multiple rows

INSERTINTO Temp ( Id, Name, Salary )

SELECT ( E_id, E_name, Salary)FROM EmpsWHERE Salary > 33000;

CREATE TABLE Temp (Id CHAR(2),Name CHAR(20),Salary DECIMAL(5),

PRIMARY KEY (Id) );

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UPDATE

UPDATE EmpsSET Salary = Salary + 900WHERE Salary < 40000;

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DELETE

DELETEFROM Depts WHERE Budget < 1000000;

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CREATE VIEW

CREATE VIEW All_emps ASSELECT (Dept_name, E_name, Salary)FROM Depts, EmpsWHERE Depts.Dept_id = Emps.Dept_id

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query a view

SELECT ( E_name, Salary )FROM All_empsWHERE Salary < 40000

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Intermediate conclusion

you now know a small set of operators by means of which you can create, query and modify a database; you can now implement your own database (even though, it probably will be far from a good design)

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Activity A4

You are the database administrator of your company. Your company is supplied with different parts by a set of supplying companies. You need to create and maintain a database with information about the supplied parts and the supplying companies.

1. given the ER (entity relationship) diagram, identify the attributes of each entity (NOTE: treat the relationship as an entity, i.e. find its attribute(s))

2. design the corresponding tables 3. write the data definition statements in SQL

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ER for the suppliers-parts problem

Supplier PartsContracted

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Conclusion

summary introduction to database systems introduction to the relational model introduction to SQL

from next lecture the relational model