SQL Presentation-1 (structured query language)

Chapter 7:
SQL, the Structured
Query Language
Soid Quintero & Ervi Bongso
CS157B

Overview
Introduction
DDL Commands
DML Commands
SQL Statements, Operators, Clauses
Aggregate Functions

The ANSI standard language for the definition
and manipulation of relational database.
Includes data definition language (DDL),
statements that specify and modify database
schemas.
Includes a data manipulation language (DML),
statements that manipulate database content.
Structured Query Language (SQL)

Some Facts on SQL
SQL data is case-sensitive, SQL commands are not.
First Version was developed at IBM by Donald D.
Chamberlin and Raymond F. Boyce. [SQL]
Developed using Dr. E.F. Codd's paper, “A Relational
Model of Data for Large Shared Data Banks.”
SQL query includes references to tuples variables
and the attributes of those variables

SQL: DDL Commands
CREATE TABLE: used to create a table.
ALTER TABLE: modifies a table after it was created.
DROP TABLE: removes a table from a database.

SQL: CREATE TABLE Statement
Things to consider before you create your table are:
The type of data
the table name
what column(s) will make up the primary key
the names of the columns
CREATE TABLE statement syntax:
CREATE TABLE <table name>
( field1 datatype ( NOT NULL ),
field2 datatype ( NOT NULL )
);

SQL: Attributes Types
Table 7.6 pg.164

SQL: ALTER TABLE Statement
To add or drop columns on existing tables.
ALTER TABLE statement syntax:
ALTER TABLE <table name>
ADD attr datatype;
or
DROP COLUMN attr;

SQL: DROP TABLE Statement
Has two options:
CASCADE: Specifies that any foreign key constraint
violations that are caused by dropping the table will
cause the corresponding rows of the related table to
be deleted.
RESTRICT: blocks the deletion of the table of any
foreign key constraint violations would be created.
DROP TABLE statement syntax:
DROP TABLE <table name> [ RESTRICT|CASCADE ];

Example:
CREATE TABLE FoodCart (
date varchar(10),
food varchar(20),
profit float
);
ALTER TABLE FoodCart (
ADD sold int
);
ALTER TABLE FoodCart(
DROP COLUMN profit
);
DROP TABLE FoodCart;
profit
food
date
sold
profit
food
date
sold
food
date
FoodCart
FoodCart
FoodCart

SQL: DML Commands
INSERT: adds new rows to a table.
UPDATE: modifies one or more attributes.
DELETE: deletes one or more rows from a table.

SQL: INSERT Statement
To insert a row into a table, it is necessary to
have a value for each attribute, and order matters.
INSERT statement syntax:
INSERT into <table name>
VALUES ('value1', 'value2', NULL);
Example: INSERT into FoodCart
VALUES (’02/26/08', ‘pizza', 70 );
FoodCart
70
pizza
02/26/08
500
hotdog
02/26/08
350
pizza
02/25/08
sold
food
date
500
hotdog
02/26/08
350
pizza
02/25/08
sold
food
date

SQL: UPDATE Statement
To update the content of the table:
UPDATE statement syntax:
UPDATE <table name> SET <attr> = <value>
WHERE <selection condition>;
Example: UPDATE FoodCart SET sold = 349
WHERE date = ’02/25/08’ AND food = ‘pizza’;
FoodCart
70
pizza
02/26/08
500
hotdog
02/26/08
350
pizza
02/25/08
sold
food
date
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date

SQL: DELETE Statement
To delete rows from the table:
DELETE statement syntax:
DELETE FROM <table name>
WHERE <condition>;
Example: DELETE FROM FoodCart
WHERE food = ‘hotdog’;
FoodCart
Note: If the WHERE clause is omitted all rows of data are deleted from the table.
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date
70
pizza
02/26/08
349
pizza
02/25/08
sold
food
date

SQL Statements, Operations, Clauses
SQL Statements:
Select
SQL Operations:
Join
Left Join
Right Join
Like
SQL Clauses:
Order By
Group By
Having

SQL: SELECT Statement
A basic SELECT statement includes 3 clauses
SELECT <attribute name> FROM <tables> WHERE <condition>
SELECT
Specifies the
attributes that are
part of the
resulting relation
FROM
Specifies the
tables that serve
as the input to the
statement
WHERE
Specifies the
selection condition,
including the join
condition.
Note: that you don't need to use WHERE

Using a “*” in a select statement indicates that
every attribute of the input table is to be
selected.
Example: SELECT * FROM … WHERE …;
To get unique rows, type the keyword
DISTINCT after SELECT.
Example: SELECT DISTINCT * FROM …
WHERE …;
SQL: SELECT Statement (cont.)

Example:
Person
80
34
Peter
54
54
Helena
70
29
George
64
28
Sally
80
34
Harry
Weight
Age
Name
80
34
Peter
54
54
Helena
80
34
Harry
Weight
Age
Name
80
54
80
Weight
1) SELECT *
FROM person
WHERE age > 30;
2) SELECT weight
FROM person
WHERE age > 30;
3) SELECT distinct
weight
FROM person
WHERE age > 30;
54
80
Weight

SQL: Join operation
A join can be specified in the FROM clause
which list the two input relations and the
WHERE clause which lists the join condition.
Example:
Biotech
1003
Sales
1002
IT
1001
Division
ID
TN
1002
MA
1001
CA
1000
State
ID
Emp Dept

SQL: Join operation (cont.)
Sales
1002
IT
1001
Dept.Division
Dept.ID
TN
1002
MA
1001
Emp.State
Emp.ID
inner join = join
SELECT *
FROM emp join dept (or FROM emp, dept)
on emp.id = dept.id;

IT
1001
Sales
1002
null
null
Dept.Division
Dept.ID
CA
1000
TN
1002
MA
1001
Emp.State
Emp.ID
left outer join = left join
SELECT *
FROM emp left join dept

Sales
1002
Biotech
1003
IT
1001
Dept.Division
Dept.ID
MA
1001
null
null
TN
1002
Emp.State
Emp.ID
right outer join = right join
SELECT *
FROM emp right join dept

SQL: Like operation
Pattern matching selection
% (arbitrary string)
SELECT *
FROM emp
WHERE ID like ‘%01’;
 finds ID that ends with 01, e.g. 1001, 2001, etc
_ (a single character)
SELECT *
FROM emp
WHERE ID like ‘_01_’;
 finds ID that has the second and third character
as 01, e.g. 1010, 1011, 1012, 1013, etc

SQL: The ORDER BY Clause
Ordered result selection
desc (descending order)
SELECT *
FROM emp
order by state desc
 puts state in descending order, e.g. TN, MA, CA
asc (ascending order)
SELECT *
FROM emp
order by id asc
 puts ID in ascending order, e.g. 1001, 1002, 1003

SQL: The GROUP BY Clause
The function to divide the tuples into groups and
returns an aggregate for each group.
Usually, it is an aggregate function’s companion
SELECT food, sum(sold) as totalSold
FROM FoodCart
group by food;
FoodCart
419
pizza
500
hotdog
totalSold
food
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date

SQL: The HAVING Clause
The substitute of WHERE for aggregate functions
Usually, it is an aggregate function’s companion
SELECT food, sum(sold) as totalSold
FROM FoodCart
group by food
having sum(sold) > 450;
FoodCart
500
hotdog
totalSold
food
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date

SQL: Aggregate Functions
Are used to provide summarization information for
SQL statements, which return a single value.
COUNT(attr)
SUM(attr)
MAX(attr)
MIN(attr)
AVG(attr)
Note: when using aggregate functions, NULL values
are not considered, except in COUNT(*) .

SQL: Aggregate Functions (cont.)
COUNT(attr) -> return # of rows that are not null
Ex: COUNT(distinct food) from FoodCart; -> 2
SUM(attr) -> return the sum of values in the attr
Ex: SUM(sold) from FoodCart; -> 919
MAX(attr) -> return the highest value from the attr
Ex: MAX(sold) from FoodCart; -> 500
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date
FoodCart

SQL: Aggregate Functions (cont.)
MIN(attr) -> return the lowest value from the attr
Ex: MIN(sold) from FoodCart; -> 70
AVG(attr) -> return the average value from the attr
Ex: AVG(sold) from FoodCart; -> 306.33
Note: value is rounded to the precision of the datatype
70
pizza
02/26/08
500
hotdog
02/26/08
349
pizza
02/25/08
sold
food
date
FoodCart

Riccardi, Greg. Principles of Database Systems with Internet and Java
Applications. Addison Wesley, 2001.
Ronald R. Plew, Ryan K. Stephens. Teach Yourself SQL in 24 Hours 3rd Edition.
Sams Publishing, 2003.
SQL http://en.wikipedia.org/wiki/SQL
W3C http://www.w3schools.com/sql/sql_tryit.asp
Wikipedia - SQL http://en.wikipedia.org/wiki/SQL
Wikipedia - join http://en.wikipedia.org/wiki/Join_(SQL)
References

SQL Presentation-1 (structured query language)

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