DBMS BRESHUP

8/2/2019 DBMS BRESHUP

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What is SQL?• SQL stands for Structured Query Language

• SQL lets you access and manipulate databases

• SQL is an ANSI (American National Standards Institute) standard

What Can SQL do?• SQL can execute queries against a database

• SQL can retrieve data from a database

• SQL can insert records in a database

• SQL can update records in a database

• SQL can delete records from a database

• SQL can create new databases

• SQL can create new tables in a database

• SQL can create stored procedures in a database

• SQL can create views in a database

• SQL can set permissions on tables, procedures, and views

SQL DML and DDLSQL can be divided into two parts: The Data Manipulation Language (DML) and the Data

Definition Language (DDL).

The query and update commands form the DML part of SQL:

• SELECT - extracts data from a database

• UPDATE - updates data in a database

• DELETE - deletes data from a database

• INSERT INTO - inserts new data into a database

The DDL part of SQL permits database tables to be created or deleted. It also defines indexes(keys), specifies links between tables, and imposes constraints between tables. The most importantDDL statements in SQL are:

• CREATE DATABASE - creates a new database

• ALTER DATABASE - modifies a database

• CREATE TABLE - creates a new table

• ALTER TABLE - modifies a table

• DROP TABLE - deletes a table

• CREATE INDEX - creates an index (search key)

• DROP INDEX - deletes an index

SQL SELECT SyntaxSELECT column_name(s)FROM table_name

and

SELECT * FROM table_name=selects the entire table.The DISTINCT keyword can be used to return only distinct (different) values.

SQL SELECT DISTINCT SyntaxSELECT DISTINCT column_name(s)

FROM table_name



now it only selects the column specified.

SQL WHERE SyntaxSELECT column_name(s)FROM table_name

WHERE column_name operator value

eg)SELECT name from customer WHERE city="downtown";now it selects the name of customer which has city as downtown.

SQL AND & OR OperatorsThe AND operator displays a record if both the first condition and the second condition is true.

The OR operator displays a record if either the first condition or the second condition is true.SELECT * FROM Persons

WHERE FirstName='Tove'

AND LastName='Svendson'

now it selects persons if his first name is tove and last name is svendsonSELECT * FROM Persons

WHERE FirstName='Tove'

OR FirstName='Ola'

now it selects persons if either his first name is tove or last name is ola

Combining AND & ORSELECT * FROM Persons WHERE

LastName='Svendson'AND (FirstName='Tove' OR FirstName='Ola')

now it selects persons who as firstname as either tove or ola and last name should be svendson

The ORDER BY Keyword The ORDER BY keyword is used to sort the result-set by a specified column.

The ORDER BY keyword sort the records in ascending order by default.

If you want to sort the records in a descending order, you can use the DESC keyword.

SQL ORDER BY SyntaxSELECT column_name(s)

FROM table_name

ORDER BY column_name(s) ASC|DESCeg)SELECT * FROM Persons

ORDER BY LastName

SQL INSERT INTO Statement

The INSERT INTO Statement The INSERT INTO statement is used to insert a new record or row in a table.

SQL INSERT INTO SyntaxIt is possible to write the INSERT INTO statement in two forms.

The first form doesn't specify the column names where the data will be inserted, only their values:

INSERT INTO table_name

VALUES (value1, value2, value3,...)

The second form specifies both the column names and the values to be inserted:



INSERT INTO table_name (column1, column2, column3,...)

VALUES (value1, value2, value3,...)eg)INSERT INTO Persons

VALUES (4,'Nilsen', 'Johan', 'Bakken 2', 'Stavanger')

eg)INSERT INTO Persons (P_Id, LastName, FirstName)VALUES (5, 'Tjessem', 'Jakob')

The UPDATE Statement

The UPDATE statement is used to update existing records in a table.

SQL UPDATE SyntaxUPDATE table_name

SET column1=value, column2=value2,...WHERE some_column=some_value

eg)UPDATE Persons

SET Address='Nissestien 67', City='Sandnes'WHERE LastName='Tjessem' AND FirstName='Jakob'

The DELETE Statement

The DELETE statement is used to delete rows in a table.

SQL DELETE SyntaxDELETE FROM table_name

WHERE some_column=some_valueeg)DELETE FROM Persons

WHERE LastName='Tjessem' AND FirstName='Jakob'

DROP:deletes the entire table

Syntax:DROP Table Name;TRUNCATE:deletes the values only but table remains

Syntax:Truncate Table Name;

SQL IN OperatorThe IN operator allows you to specify multiple values in a WHERE clause.

SQL IN SyntaxSELECT column_name(s)

FROM table_nameWHERE column_name IN (value1,value2,...)

eg)SELECT * FROM Persons

WHERE LastName IN ('Hansen','Pettersen')now it selects the persons with lastname either hansen or pettersen

SQL JOIN The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a

relationship between certain columns in these tables.

• JOIN: Return rows when there is at least one match in both tables

• LEFT JOIN: Return all rows from the left table, even if there are no matches in the right

table



• RIGHT JOIN: Return all rows from the right table, even if there are no matches in the lefttable

• FULL JOIN: Return rows when there is a match in one of the tables

SQL INNER JOIN Keyword The INNER JOIN keyword return rows when there is at least one match in both tables.

SQL INNER JOIN Syntax

SELECT column_name(s)FROM table_name1

INNER JOIN table_name2

ON table_name1.column_name=table_name2.column_name

SQL INNER JOIN ExampleThe "Persons" table:

P_Id LastName FirstName Address City

1 Hansen Ola Timoteivn 10 Sandnes

2 Svendson Tove Borgvn 23 Sandnes

3 Pettersen Kari Storgt 20 Stavanger

The "Orders" table:

O_Id OrderNo P_Id

1 77895 3

2 44678 3

3 22456 1

4 24562 1

5 34764 15

Now we want to list all the persons with any orders.

We use the following SELECT statement:

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM Persons

INNER JOIN Orders

ON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName

The result-set will look like this:

LastName FirstName OrderNo

Hansen Ola 22456

Hansen Ola 24562

Pettersen Kari 77895




The INNER JOIN keyword return rows when there is at least one match in both tables. If there are

rows in "Persons" that do not have matches in "Orders", those rows will NOT be listed.

SQL LEFT JOIN Keyword The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no

matches in the right table (table_name2).

SQL LEFT JOIN Syntax

SELECT column_name(s)FROM table_name1

LEFT JOIN table_name2


PS: In some databases LEFT JOIN is called LEFT OUTER JOIN.

SQL LEFT JOIN ExampleThe "Persons" table:





The "Orders" table:

O_Id OrderNo P_Id

1 77895 3

2 44678 3

3 22456 1

4 24562 1

5 34764 15

Now we want to list all the persons and their orders - if any, from the tables above.


SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo

FROM PersonsLEFT JOIN Orders

ON Persons.P_Id=Orders.P_Id

ORDER BY Persons.LastName



Hansen Ola 22456

Hansen Ola 24562





Svendson Tove

The LEFT JOIN keyword returns all the rows from the left table (Persons), even if there are no

matches in the right table (Orders).

SQL RIGHT JOIN Keyword The RIGHT JOIN keyword returns all the rows from the right table (table_name2), even if thereare no matches in the left table (table_name1).

SQL RIGHT JOIN Syntax

SELECT column_name(s)

FROM table_name1RIGHT JOIN table_name2


PS: In some databases RIGHT JOIN is called RIGHT OUTER JOIN.

SQL RIGHT JOIN ExampleThe "Persons" table:





The "Orders" table:

O_Id OrderNo P_Id

1 77895 3

2 44678 3

3 22456 1

4 24562 1

5 34764 15

Now we want to list all the orders with containing persons - if any, from the tables above.


SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo

FROM Persons

RIGHT JOIN OrdersON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName



Hansen Ola 22456

Hansen Ola 24562





34764

The RIGHT JOIN keyword returns all the rows from the right table (Orders), even if there are no

matches in the left table (Persons).

SQL FULL JOIN Keyword The FULL JOIN keyword return rows when there is a match in one of the tables.

SQL FULL JOIN Syntax


FROM table_name1FULL JOIN table_name2


SQL FULL JOIN ExampleThe "Persons" table:

P_Id LastName FirstName Address City1 Hansen Ola Timoteivn 10 Sandnes



The "Orders" table:

O_Id OrderNo P_Id

1 77895 3

2 44678 3

3 22456 1

4 24562 1

5 34764 15

Now we want to list all the persons and their orders, and all the orders with their persons.We use the following SELECT statement:

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM Persons

FULL JOIN Orders

ON Persons.P_Id=Orders.P_Id

ORDER BY Persons.LastName



Hansen Ola 22456

Hansen Ola 24562





Svendson Tove

34764

The FULL JOIN keyword returns all the rows from the left table (Persons), and all the rows fromthe right table (Orders). If there are rows in "Persons" that do not have matches in "Orders", or if

there are rows in "Orders" that do not have matches in "Persons", those rows will be listed as well.

The SQL UNION Operator The UNION operator is used to combine the result-set of two or more SELECT statements.

SQL UNION Syntax

SELECT column_name(s) FROM table_name1

UNION

SELECT column_name(s) FROM table_name2

Note: The UNION operator selects only distinct values by default. To allow duplicate values, use

UNION ALL.

SQL UNION ALL SyntaxSELECT column_name(s) FROM table_name1

UNION ALLSELECT column_name(s) FROM table_name2

here duplication is allowed

SQL ConstraintsConstraints are used to limit the type of data that can go into a table.Constraints can be specified when a table is created (with the CREATE TABLE statement) or after

the table is created (with the ALTER TABLE statement).

• NOT NULL

• UNIQUE

• PRIMARY KEY

• FOREIGN KEY

• CHECK

• DEFAULT

The NOT NULL constraint enforces a column to NOT accept NULL values.

UNIQUE KEY:

The UNIQUE constraint uniquely identifies each record in a database table.

The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a

column or set of columns.A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it.

Note that you can have many UNIQUE constraints per table, but only one PRIMARY KEYconstraint per table.

SQL PRIMARY KEY Constraint The PRIMARY KEY constraint uniquely identifies each record in a database table.

Primary keys must contain unique values.

A primary key column cannot contain NULL values.Each table should have a primary key, and each table can have only ONE primary key.



SQL FOREIGN KEY Constraint A FOREIGN KEY in one table points to a PRIMARY KEY in another table.




3 Pettersen Kari Storgt 20 Stavanger The "Orders" table:

O_Id OrderNo P_Id

1 77895 3

2 44678 3

3 22456 2

4 24562 1

Note that the "P_Id" column in the "Orders" table points to the "P_Id" column in the "Persons"table.

The "P_Id" column in the "Persons" table is the PRIMARY KEY in the "Persons" table.

The "P_Id" column in the "Orders" table is a FOREIGN KEY in the "Orders" table.The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables.

SQL INDEX:used for fast searching.

SQL CREATE INDEX SyntaxCreates an index on a table. Duplicate values are allowed:

CREATE INDEX index_name

ON table_name (column_name)

SQL CREATE UNIQUE INDEX SyntaxCreates a unique index on a table. Duplicate values are not allowed:

CREATE UNIQUE INDEX index_name ON table_name (column_name);

SQL CREATE VIEW Statement In SQL, a view is a virtual table based on the result-set of an SQL statement.

A view contains rows and columns, just like a real table. The fields in a view are fields from one or

more real tables in the database.

You can add SQL functions, WHERE, and JOIN statements to a view and present the data as if thedata were coming from one single table.

SQL CREATE VIEW SyntaxCREATE VIEW view_name AS


FROM table_nameWHERE condition;



Super KeyA Super key is any combination of fields within a table that uniquely identifies each record within

that table.

Candidate KeyA candidate is a subset of a super key. A candidate key is a single field or the least combination of

fields that uniquely identifies each record in the table. The least combination of fields distinguishesa candidate key from a super key. Every table must have at least one candidate key but at the same

time can have several.SQL AGGREGATE FUNCTIONS:

1.COUNT

2.AVERAGE

3.MIN

4.MAX

SALES

OrderID OrderDate OrderPrice OrderQuantity CustomerName

1 12/22/2005 160 2 Smith

2 08/10/2005 190 2 Johnson

3 07/13/2005 500 5 Baldwin

4 07/15/2005 420 2 Smith

5 12/22/2005 1000 4 Wood

6 10/2/2005 820 4 Smith

7 11/03/2005 2000 2 Baldwin

SELECT COUNT (*) FROM Sales

WHERE CustomerName = 'Smith'

ans:3it rettuns the no of rows which satisfies the given condition

SELECT SUM(OrderPrice) FROM Sales

it adds the values in order price column and returns the resultSELECT AVG(OrderQuantity) FROM Sales

it returns the average of orderquantity

SELECT MIN(OrderPrice) FROM Salesreturns the minimun numeric value in specified column

SELECT MAX(OrderPrice) FROM Sales

returns the maximum numeric value in specified column

NORMALIZATION: Normalization is the process of efficiently organizing data in a database. There are two goals of the

normalization process: eliminating redundant data (for example, storing the same data in more than

one table) and ensuring data dependencies make sense (only storing related data in a table).

http://databases.about.com/library/glossary/bldef-table.htm

http://databases.about.com/od/specificproducts/a/Database-Dependency.htm

http://databases.about.com/library/glossary/bldef-table.htm




First Normal Form (1NF)First normal form (1NF) sets the very basic rules for an organized database:

• Eliminate duplicative columns from the same table.

• Create separate tables for each group of related data and identify each row with a unique

column or set of columns (the primary key).

Second Normal Form (2NF)Second normal form (2NF) further addresses the concept of removing duplicative data:

• Meet all the requirements of the first normal form.

• Remove subsets of data that apply to multiple rows of a table and place them in separate

tables.

• Create relationships between these new tables and their predecessors through the use of foreign keys.

Third Normal Form (3NF)Third normal form (3NF) goes one large step further:

• Meet all the requirements of the second normal form.

•Remove columns that are not dependent upon the primary key.

For more details, read Putting your Database in Third Normal Form

Boyce-Codd Normal Form (BCNF or 3.5NF)The Boyce-Codd Normal Form, also referred to as the "third and half (3.5) normal form", adds one

more requirement:

• Meet all the requirements of the third normal form.

• Every determinant must be a candidate key.

Fourth Normal Form (4NF)Finally, fourth normal form (4NF) has one additional requirement:

• Meet all the requirements of the third normal form.

• A relation is in 4NF if it has no multi-valued dependencies.Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must

first fulfill all the criteria of a 1NF database.

http://databases.about.com/library/glossary/bldef-column.htm

http://databases.about.com/library/glossary/bldef-row.htm

http://databases.about.com/library/glossary/bldef-primarykey.htm

http://databases.about.com/library/glossary/bldef-foreignkey.htm


http://databases.about.com/od/specificproducts/l/aa3nf.htm

http://databases.about.com/cs/specificproducts/g/candidate.htm

http://databases.about.com/od/specificproducts/g/multivalued-dependency.htm


http://databases.about.com/library/glossary/bldef-column.htm

http://databases.about.com/library/glossary/bldef-row.htm

http://databases.about.com/library/glossary/bldef-primarykey.htm

http://databases.about.com/library/glossary/bldef-foreignkey.htm


http://databases.about.com/od/specificproducts/l/aa3nf.htm

http://databases.about.com/cs/specificproducts/g/candidate.htm


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