CS 377

Database Systems

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Relational Calculus and SQL

Li Xiong

Department of Mathematics and Computer Science

Emory University

Outline� Relational Algebra

� Relational Calculus� Tuple Relational Calculus

� SQL

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Relational Calculus

� A relational calculus is a declarative language for specifying database queries� tuple relational calculus

� domain relational calculus

� Relational calculus vs. relational algebra� Relational calculus is nonprocedural. A calculus

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� Relational calculus is nonprocedural. A calculus expression specifies what is to be retrieved rather than how to retrieve it

� Relational algebra is procedural. A relational algebra expression contains a sequence of operations to specify a retrieval request.

� Relational calculus and relational algebra are logically

equivalent

Tuple Relational Calculus� A simple tuple relational calculus query is of the form

{t | COND(t)}

where t is a tuple variable and COND (t) is a conditional expression involving t. The result of such a query is the set of all tuples t that satisfy COND (t)

� Example:

To find the first and last names of all employees whose salary is above $50,000

{t.FNAME, t.LNAME | EMPLOYEE(t) AND t.SALARY>50000}

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{t.FNAME, t.LNAME | EMPLOYEE(t) AND t.SALARY>50000}

� General expression

� Range relation

� Attributes

� Selection/join conditions

The Existential and Universal Quantifiers

� Two special quantifiers can appear in formulas

� universal quantifier (∀∀∀∀)

� existential quantifier (∃∃∃∃).

� Informally, a tuple variable t is bound if it is quantified, meaning that it

appears in an (∀∀∀∀ t) or (∃∃∃∃ t) clause; otherwise, it is free.

� The only free tuple variables in a tuple relational calculus expression should be those that appear to the left of |

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be those that appear to the left of |

� (∃∃∃∃ t)(F) is true if F evaluates to true for some (at least one) tuple t; otherwise false.

� (∀∀∀∀ t)(F) is true if F evaluates to true for every tuple (in the universe) t; otherwise false.

Sample Queries in Tuple

Relational Calculus

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Sample Queries in Tuple

Relational Calculus(For all projects, they are either not controlled by department 5 or e is working on)

Q3: {e.lname, e.fname | Employee(e)

AND ((∀∀∀∀x) (NOT (Project(x))

OR NOT (x.dnum = 5)

OR ((∃∃∃∃w) (Works_on(w)

AND w.essn =e.ssn

AND x.pnumber = w.pno))))}

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AND x.pnumber = w.pno))))}

(There is no project controlled by dept 5 that e is not working on)

Q3A: {e.lame, e.fname | Employee(e)

AND (NOT (∃∃∃∃x) (Project (x) AND (x.dnum = 5)

AND (NOT (∃∃∃∃w) (Works_on(w)

AND w.essn = e.ssn

AND x.pnumber = w.pno))))}

Outline� Relational Algebra

� Relational Calculus� Tuple Relational Calculus

� SQL

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Requirement analysis

Requirement specification

Conceptual design

Conceptual data model (ER Model)

Logical design

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Logical design

Representational data model (Relational Model)

Physical design

Physical data model

Database design implementation Data definition/manipulation (SQL)

SQL Introduction� SQL (Structured Query Language) – create,

retrieve, update and delete data from relational

database systems

� A data manipulation language (DML) and a data

definition language (DDL)

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definition language (DDL)

Database products containing letters of SQL:

MySQL, PostreSQL, Microsoft SQL Server, SQLite

SQL vs. Relational Model

� Important distinction between SQL and the formal relational

model

� An SQL relation (table) is a multi-set (bag) of tuples; it is not a set

of tuples

� SQL relations can be constrained to be sets by specifying PRIMARY

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SQL relations can be constrained to be sets by specifying PRIMARY KEY or UNIQUE attributes, or by using the DISTINCT option in a query

SQL and Relational Calculus

� The language SQL is inspired by tuple relational

calculus.

� SQL is a declarative language to a great extent

� Basic SQL block structure

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SELECT <list of attributes>

FROM <list of relations>

WHERE <conditions>

� General relational calculus expression

� Range relation

� Attributes

� conditions

SQL and relational algebra� Execution of a SQL query is based on relational

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Query plan in relational algebra� A query plan is a relational algebra expression represented as a query tree

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Using SQL

� Stand-alone (CLI or GUI): SQL*Plus (see tutorial)

� Embedded in a host language (C, C++, Java, etc.)

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SQL Outline

� Data definition

� Query

� Data update

� View definition

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� View definition

Data Definition

� Define a database schema

� Create new relations (tables) in a schema

� Alter the structure of existing relations

� Delete relations

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� Delete relations

CREATE SCHEMA

� Define a database schema, which is used to group

database tables and other constructs that belong to

the same database application

� Syntax

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� Syntax

CREATE SCHEMA schema_name AUTHORIZATION

db_user;

� Typically executed by DBA who will grant

authorities to some database user who then owns

the database schema

CREATE TABLE� Specifies a new base relation by giving it a name, and specifying each of

its attributes and their data types

� Syntax:

CREATE TABLE relation_name

( attr_name1 type1 [attr_constraint1] ,

....

attr_namen typen [attr_constraintn]

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attr_namen typen [attr_constraintn]

[ , integrity constrains ]

);

� Example:CREATE TABLE DEPARTMENT( DNAME VARCHAR(10) NOT NULL,

DNUMBER INTEGER NOT NULL,MGRSSN CHAR(9),MGRSTARTDATE CHAR(9) );

� Create a new table from existing table

CREATE TABLE AS QUERY (later)

Data Types� Numeric Types:

� INTEGER or INT - integer

� SMALLINT - short integer

� DECIMAL(i,j) or DEC(i,j) or NUMERIC(i,j) - fixed point numbers with i decimal digits and j digits after the decimal point. E.g.: DEC(8,3): xxxxx.yyy

� FLOAT or REAL - single precision floating point numbers (with roundoff errors)

� DOUBLE PRECISION - double precision floating point numbers (still with roundoff errors)

� Character string� CHARACTER(n) or CHAR(n) - fixed length character strings

� VARCHAR(n) or CHAR VARYING(n) or CHARACTER VARYING(n) - To denote string: 'John'

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VARCHAR(n) or CHAR VARYING(n) or CHARACTER VARYING(n) - To denote string: 'John'

� Bit string� BIT(n) - fixed length bit string

� BIT VARYING(n) - variable length bit string - To denote bit string: B'10101'

� BOOLEAN - boolean data NOTE: Due to the NULL value, SQL uses a three value logic

� DATE - Calendar date NOTE: DATE values are specified as: DATE'YYYY-MM-DD‘, must be preceded by the keyword DATE

� TIME - Time of day NOTE: TIME values are specified as: TIME'HH:MM:SS‘, Must be preceded by the keyword TIME

� TIMESTAMP - DATA + TIME NOTE: TIMESTAMP values are specified as: TIMESTAMP'YYYY-MM-DD HH:MM:SS'

Specifying Constraints

� Attribute constraints� not null

� attribute domain

� default values

� Key attributes

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Key attributes

� Referential integrity constraints (foreign keys)

Attribute Constraints

� NOT NULL: attribute cannot be assigned a NULL value

� Example: CREATE TABLE test

( ssn CHAR(9) NOT NULL,

fname CHAR(30), .... );

Insert into test(fname, lname) values (‘John’, ‘Smith’); ?

� DEFAULT: specify a default value of an attribute

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� DEFAULT: specify a default value of an attribute

� Example: CREATE TABLE test

( ssn CHAR(9) NOT NULL,

salary DECIMAL(6,2) DEFAULT 50000, .... );

insert into test(ssn) values ('111223333'); ?

� If no DEFAULT value is specified, the default value is NULL

� CHECK: check if the value of an attribute is within a specific range

� Example: CREATE TABLE test

( ssn CHAR(9) NOT NULL,

dno INTEGER CHECK (dno > 0 AND dno < 21));

Key Constraints

� The Primary Key attribute can be specified by primary

key constraint.

� The UNIQUE constraint can be used to specify candidate

keys

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CREATE TABLE DEPT

( DNAME VARCHAR(10) NOT NULL,

DNUMBER INTEGER NOT NULL,

MGRSSN CHAR(9),

MGRSTARTDATE CHAR(9),

PRIMARY KEY (DNUMBER),

UNIQUE (DNAME),

FOREIGN KEY (MGRSSN) REFERENCES EMP );

Referential Constraints

� The Foreign Key attribute is used to reference (i.e., identify) tuples in anotherrelation and as such, the referenced tuples must exist to maintain integrity

� Each key constraint may be (and better be) identified by a constraint name

� Example: CREATE TABLE employee

( ssn CHAR(9) NOT NULL,

....

CONSTRAINT Test1PrimKey PRIMARY KEY(ssn)

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CONSTRAINT Test1PrimKey PRIMARY KEY(ssn)

);

CREATE TABLE dependent

( essn CHAR(9) NOT NULL,

...

CONSTRAINT Test2ForeignKey FOREIGN KEY (essn)

REFRENCES employee(ssn)

);

� insert into dependent values ('111223333’); ?

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Chicken and Egg Problem?

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� Cannot define a referential integrity constraint when

the referenced attribute does not exist

� Solution: using the ALTER command to add the

referential constraints relations are created

Alter Table

� Adding attributes

� Removing attributes

� Adding constraints

� Removing constraints

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� Removing constraints

� Rename/update attributes? - No

ALTER TABLE – Add Attributes

� Used to add an attribute to one of the base relations

� The new attribute will have NULLs in all the tuples of the relation right

after the command is executed; hence, the NOT NULL constraint is not

allowed for such an attribute

� Example:

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ALTER TABLE EMPLOYEE ADD JOB VARCHAR(12);

� The database users must still enter a value for the new attribute JOB for

each EMPLOYEE tuple. This can be done using the UPDATE

command.

ALTER TABLE – Remove Attributes

� ALTER TABLE table_name DROP [COLUMN] attr_name{RESTRICTED|CASCADE};

� RESTRICTED: only the attribute table_name.attr_name is dropped -however, if the attribute table_name.attr_name is a part of a foreign key in some other relation, it cannot be dropped.

� E.g. You cannot drop employee.ssn because it is used as a foreign key in dependent department

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E.g. You cannot drop employee.ssn because it is used as a foreign key in dependent, department, etc

� CASCADE: the attribute table_name.attr_name is dropped and if the attribute table_name.attr_name is a part of a foreign key in some other relation, that attribute will also be dropped, and so on

ALTER Table – Add/Remove

Constraints� Adding a new constraint

ALTER TABLE table_name ADD CONSTRAINT constraint_name

constraint_def;

� Example: ALTER TABLE employee ADD CONSTRAINT

EmpPrimKey ssn PRIMARY KEY(ssn);

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� NOTE: If there are some tuples in the relation, and the constraint is

violated by some tuples, the new constraint is NOT recorded.

� Removing an existing constraint

ALTER TABLE table_name DROP CONSTRAINT constraint_name ;

� Example: ALTER TABLE employee DROP CONSTRAINT

EmpPrimKey;

� NOTE: you can only drop a constraint if you have given it a name at

the time of definition.

Solve the Chicken and Egg ProblemCREATE TABLE employee

( ssn CHAR(9),

....

CONSTRAINT EmpPrimKey

PRIMARY KEY (ssn),

);

CREATE TABLE department

( dnumber INT,

....

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....

mgrssn CHAR(9),

CONSTRAINT DepPrimKey

PRIMARY KEY (dnumber),

CONSTRAINT MgrForeignKey

FOREIGN KEY (mgrssn)

REFRENCES employee(ssn)

);

ALTER TABLE employee ADD

CONSTRAINT DepForeignKey

FOREIGN KEY dno

REFERENCES department(dnumber);

How can we insert any new tuple

into the relations without violating

the referential constraints?

Chicken and Egg Problem Round 2?

� Solution:

ALTER TABLE emp

DROP CONSTRAINT DepForeignKey;

ALTER TABLE emp

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ALTER TABLE emp

ADD CONSTRAINT DepForeignKey

FOREIGN KEY (dno)

REFERENCES dept(dnumber)

INITIALLY DEFERRED DEFERRABLE;

INSERT INTO emp VALUES ('444444444', 12);

INSERT INTO dept VALUES (12, '444444444');

COMMIT;

DROP TABLE

� Used to remove a relation (base table) and its

definition

� The relation can no longer be used in queries,

updates, or any other commands since its

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updates, or any other commands since its

description no longer exists

� DROP TABLE table_name;

� DROP TABLE table_name cascade constraints;

Creating Company Database and

Loading Data� Create tables using SQL

� Load data using SQL Loader (see tutorial)

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Outline

� Data definition

� Query

� Data update

� View definition

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� View definition