CS2300: File Structures and

Introduction to Database Systems

Lecture 15: SQL

Doug McGeehan

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Brief Review

• Create tables

– Specify various constraints on table and attributes

• Drop tables

– RESTRICT• Drop table if it is not referenced

– CASCADE• Drop constraints that depend on the table

• Then drop data and remove table

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Brief Review

• Create tables

– Specify various constraints on table and attributes

• Drop tables

– Note for MySQL / MariaDB:• RESTRICT and CASCADE have no effect

• DROP TABLE eliminates referential integrity constraints

i.e. foreign keys revert back to plain attributes

Creating Your Database

• In MySQL / MariaDB

– Root account

• Allows control over entire database

• Password is set up upon installation

• Permits the creation of new databases

– Unlikely you’ll be able to use MySQL

databases on the CLC Linux Machines

– Install MySQL / MariaDB server on your

own systems4

Creating Your Database

• Creating a Database in MySQL/MariaDB

– Log in with the root account

$ mysql --user root --passwordEnter password:mysql>

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Creating Your Database

• Creating a Database in MySQL/MariaDB

mysql> CREATE DATABASE CS2300;Query OK, 1 row affected (0.00 sec)

mysql> USE DATABASE CS2300;Database changedmysql>

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Creating A User

• Adding users is more secure than

accessing database through root user

mysql> GRANT ALL PRIVILEGES -> ON CS2300.* TO->'your_project_name'@->'localhost' IDENTIFIED BY->'some_password';

• Ctrl + D to exit 7

Creating A User

• Log in with your newly created user

$ mysql -u your_project_name\–p[some_password]\CS2300

mysql>

• You are in.

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Insert, Delete and Update

Data in a Table

Inserting a Row

To insert a row into the Employee table

Employee(id:integer,fname:varchar(20),gender:varchar(1),

deptnumber:integer, salary:integer)

• Approach 1:– Number of values equals airty (degree/column count) of table

– Order and types of attributes match table schema

– Result: No need to specify attribute names on Employee

SQL> Insert Into Employee

Values (122,‘Bob','M',12,110000);

Inserting a Row

To insert a row into the Employee table

Employee(id:integer,fname:varchar(20),gender:varchar(1),

deptnumber:integer, salary:integer)

• Approach 2:– Not all attribute values are defined for insertion

– Result: specify which attributes are being assigned

SQL> Insert Into Employee(id,deptnumber)Values(123,13);

Inserting a Row

• Approach 3:

– Use a SQL query to retrieve data from other tables

– Then insert them into target table

SQL> Insert Into Employee(id,fname)

Select [attr1], [attr2]

From [table_name]

Where [condition];

Inserting a Row

The insertion operation will be rejected if it

violates the constraints specified in the

table definition.

Deleting Rows

• General format:

DELETE FROM Table WHERE Condition;

• Deletes all rows satisfying Condition

from Table

Example

• Remove the employee with id 121 from the Employee

table:

DELETE FROM Employee WHERE id = 121;

• Remove all employees having a salary greater than

100,000:

DELETE FROM Employee WHERE Salary > 100000;

• Remove all records in the Employee tableDELETE FROM Employee;

Deleting Rows

• The Condition can also involve SQL

queries.

• Example:

DELETE FROM Employee

WHERE Deptnumber IN (Select Dnumber

From Department

Where Dname = `Research’);

Updating Rows

• We can update rows in a table

• General format:

UPDATE Table

SET Column1=value1,…,ColumnN=valueN

WHERE Condition

Example

• Now we can reduce salaries instead of firing employees:

UPDATE Employee

SET Salary = 100000

WHERE Salary > 100000;

Updating Rows

• The Condition can also involve SQL

queries.

• Example:

UPDATE Employee

SET Salary = Salary*1.1

WHERE Deptnumber IN (Select Dnumber

From Department

Where Dname = `Research’);

Try This Command

• Show the structure of a table

desc table_name;

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Comments?

CREATE TABLE Employee(

ID INTEGER,

Fname VARCHAR(20),

Lname VARCHAR(20),

Gender CHAR(1),

Salary INTEGER NOT NULL,

Dept INTEGER,

PRIMARY KEY(FNAME,LNAME)

);

CREATE TABLE Employee(

ID INTEGER,

Fname VARCHAR(20) PRIMARY KEY,

Lname VARCHAR(20) PRIMARY KEY,

Gender CHAR(1),

Salary INTEGER NOT NULL,

Dept INTEGER,

);

wrong

Some more constraints in

CREATE TABLE

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CHECK Conditions

• A check condition is a Boolean expression:

– E.g.: x>5 and x<10

• Attribute-Based Check

• Tuple-Based Check

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Attribute-Based Check

• Follow an attribute by a condition that

must hold for that attribute in each tuple

of its relation.

• Condition is checked only when the

associated attribute changes (i.e., an

insert or update occurs).

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Attribute-Based Check

CREATE TABLE Employee(ID INTEGER primary key,Fname VARCHAR(20),Lname VARCHAR(20),Gender CHAR(1) check(Gender=‘F’ or

Gender=‘M’),Salary INTEGER check(Salary>=0),DeptNumber INTEGER

);

The check occurs only when we insert or update an

Employee tuple, not when we delete a tuple.

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Tuple-Based Check

• Separate element of table declaration.

• Checked whenever a tuple is inserted or

updated.

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Example

• Only Joe's Bar can sell beer for more

than $5.

CREATE TABLE Sells (

bar CHAR(20),

beer CHAR(20),price REAL,PRIMARY KEY (bar,beer),

CHECK (bar = 'Joe''s Bar' OR price <= 5.00));

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Altering Tables

• Table definitions can be altered after their creation

• Use the reserved words ALTER TABLE• Options:

– Adding columns: ADD COLUMN– Changing columns’ definition: ALTER COLUMN– Dropping columns: DROP COLUMN– Adding or dropping constraints: ADD, DROP

CONSTRAINT– And more…

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Altering Tables

• Adding a column:

ALTER TABLE Employee ADD COLUMN mname VARCHAR(20);

• Changing columns’ definition:

ALTER TABLE Employee Modify mname varchar(10);

• Dropping columns:

ALTER TABLE Employee DROP COLUMN Mname CASCADE;

• Adding constraints:

ALTER TABLE Employee ADD check(age>0);

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SQL Queries

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Basic SQL Query Structure

SELECT Attributes

FROM relations

WHERE condition

SELECT sid,sname

FROM students

WHERE sid=1122

For example

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Query Components

• A query can contain the following clauses

– Select

– From

– Where

– Group by

– Having

– Order by

• Only Select and From are obligatory

• Order of clauses is always as above

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Very Basic SQL Query

SELECT [Distinct] Attributes

FROM relations

•Attributes: The attributes which will appear in the

query result (For example: id, name).

•Relations: Relations to perform the query on.

•DISTINCT: Optional keyword to delete duplicates

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StudentID StudentDept StudentName StudentAge

1123 Math Moshe 25

2245 Computers Mickey 26

55611 Math Menahem 29

Select studentID, studentName

From students

StudentID StudentName

1123 Moshe

2245 Mickey

55611 Menahem

Example

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Basic SQL Query

SELECT [Distinct] Attributes

FROM relations

WHERE condition

•condition:

– A Boolean condition

e.g. eid>21, or ename=‘Yuval’

– Only tuples satisfying condition

appear in the result

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StudentID StudentDept StudentName StudentAge

1123 Math Moshe 20

2245 NULL Mickey 18

55611 Math Menahem 21

Select studentID, studentName

From students

Where StudentDept=`Math’

StudentID StudentName

1123 Moshe

55611 Menahem

Example

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The WHERE Clause

• Numerical and string comparison:

!=,<>,=, <, >, >=, <=, between(val1 AND val2)

• Logical components: AND, OR

• Null verification: IS NULL, IS NOT NULL

• Checking against a list with IN, NOT IN

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Example

SELECT StudentName

FROM Students

WHERE age>=17 AND StudentDept IS NOT NULL ;

StudentID StudentDept StudentName StudentAge

1123 Math Moshe 20

2245 NULL Mickey 18

55611 Math Menahem 21

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Example

SELECT StudentID, StudentName

FROM Students

WHERE StudentID IN (1123,2245) OR

StudentName between(‘Alice’ and ‘Karl’);

StudentID StudentDept StudentName StudentAge

1123 Math Moshe 20

2245 NULL Mickey 18

55611 Math Bob 21

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The LIKE Operator

• A pattern matching operator (regular

expression)

• Basic format: colname LIKE pattern

• Example:

_ is a single character % is 0 or more characters

SELECT StudentName

FROM Students

WHERE StudentName LIKE ‘M%e_’;

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A Few SELECT Options

• Select all columns:SELECT * FROM Students;

• Applying functions (e.g., Mathematical manipulations)

SELECT 2010-StudentAge

FROM Students;

• Rename relations and selected columns:SELECT StudentName AS Name

FROM Students [AS] S; (here AS is optional)

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What if more than one relation

are needed for a query?

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Example

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sid sname rating age

22 dustin 7 45.0

31 lubber 8 55.5

58 rusty 10 35.0

sid bid day

22 101 10/10/96

58 103 11/12/96

Find the names of the sailors who reserved a boat.

ReserveSailor

Πsname ( sailor.sid=reserve.sid(Sailor x Reserve))

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Basic SQL Query

• If more than one relation is mentioned, the

operation is on the Cartesian product

between the relations

• Example:

Select sname

From sailor, reserve

Where sailor.sid=reserve.sid

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Relation Naming

SELECT S.sname

FROM Sailors [AS] S, Reserves [AS] R

WHERE S.sid = R.sid;

• Naming relations is good style

• It is necessary if the same relation appears

twice in the FROM clause

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SQL and Relational Algebra

SELECT Distinct A1,…,An

FROM R1,…,Rm

WHERE C;

A1,…,An(C(R1 x R2…x Rm))

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Basic SQL Query

SELECT [Distinct] attributes

FROM relations

WHERE condition;

Important! The evaluation order is:

1. Compute the cross product of the tables in relations.

2. Delete all rows that do not satisfy condition.

3. Delete all columns that do not appear in attributes.

4. If Distinct is specified, eliminate duplicate rows.

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Sailor Reserve

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 1: Sailor x Reserve

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Sailor Reserve

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Stage 2: “where sailor.sid=reserve.sid”

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Sname

Dustin

Rusty

Stage 3: “select sname”

Final answer

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Example Query

SELECT sname AS Sailor_Name

FROM Sailor S, Reserve R

WHERE S.sid = R.sid and

bid = 103;

Sailor(sid, sname, rating, age)

Reserve(sid,bid,day)

Q: Find the names of sailors who reserved boat 103

Don’t forget to include the expression highlighted by red color

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Sailor Reserve

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

WHERE S.sid = R.sid and bid = 103;

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Sailors Reserves

sid sname rating age sid bid day

22 Dustin 7 45.0 22 101 10/10/96

22 Dustin 7 45.0 58 103 11/12/96

31 Lubber 8 55.5 22 101 10/10/96

31 Lubber 8 55.5 58 103 11/12/96

58 Rusty 10 35.0 22 101 10/10/96

58 Rusty 10 35.0 58 103 11/12/96

Select sname

Exercise

• Suppliers(sid, sname, address)

• Parts(pid,pname,color)

• Catalog(sid,pid,cost)

Write the SQL query to find the names of

the suppliers who produce red parts.

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What’s Next…

• More SQL

• Project Phase 2: due Tuesday Nov 6th

at 11:59pm on Canvas

• Homework 3 assigned

– Due Thursday, Nov 1st

– Hard copy in class, Digital copy on Canvas

• Quiz 3: Thursday, Nov 1st

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