Database Query and SQL

7/30/2019 Database Query and SQL

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Ms AccessMs Access


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What is Microsoft Access?What is Microsoft Access?

Microsoft Access is a relational database

management system (DBMS or RDBMS). At the

very core, it is a software engine that provides an

interface between physical data and user.

Other examples of DBMS applications include:

OraclemySQL

SQL Server (Microsoft)

DB2 (IBM)

Informix


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Why choose MSWhy choose MS--Access over SPSS /Access over SPSS /

Excel?Excel?Although there is always overlap, the following rules might help

when deciding when / when not to use MS Access:

MS Access is best used for long-term data storage and/or data

sharing.

MS Excel is best used for minor data collection, manipulation, and

especially visualization.

SPSS is best used for minor data collection and especially dataanalysis.

It is easy to export data from MS Access to Excel SPSS


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Why choose MSWhy choose MS--Access over otherAccess over other

DBMS systems?DBMS systems?

Cheap, readily available (packaged with MS-Office

Premium).

Eas to use relative to other s stems Oracle ma

require one FTE to maintain the server as a database

administrator and another FTE to serve as an

application developer).

Includes front-end tools for rapid application

development (RAD). This also makes MS-Access a

good prototype environment.


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Why choose other DBMS systemsWhy choose other DBMS systems

over MSover MS--Access?Access?

MS-Access can handle a large number of records, but

is somewhat slow compared to some of the high-end

platforms.

Multiple users may use the database simultaneously,

but MS-Access is known to become unstable with

greater than 3-5 users.


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What is in an MSWhat is in an MS--Access file ?Access file ?

Although the term database typically refers to a

collection of related data tables, an Access databaseincludes more than just data. In addition to tables,

you can add:

Saved queries (stored procedures) - organizingand/or manipulating data

Forms GUI interaction with data, eventprogrammingReports customized results for printing

Macros and VB programs for extending functionality


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Table RelationshipsTable Relationships

One of the most powerful features of arelational database management system is

its ability to define relationships between

tables

Use a common field to relate one table to

another


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There are three basic types of relationships

One-to-One Relationship

One-to-Many Relationship

Many-to-Many Relationship


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One-to-One Relationship

A relationship between two tables where both the primary key and the

foreign key are unique in considered one-to-one. For each record in the

first table, there will be one and only one record in the second table.

In a one-to-one relationship, each record in the primary table can have

only one matching record in the foreign table and each record in the

foreign table can have only one matching record in the primary table.

A one-to-one relationship is created if both of the related fields are

primary keys or have unique indexes.


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One-to-many Relationship

A one-to-many relationship existsbetween two tables when one record in

the first table matches zero, one, or manrecords in the second table, and whenone record in the second table matches

at most one record in the first table The Primary table is the one in a one-to-

many relationship

The Related table is the many table


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Referential integrity is a set of rules

that Access enforces to maintainconsistency between related tables whenyou update data in a database

The Relationships window illustrates

the relationships among a databasestables

Click the Database Tools tab on the

Ribbon In the Show/Hide group on the Database

Tools tab, click the Relationships button


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Many-to-Many Relationship

A relationship between two tables when many records in one table can

relate to many records in another table is considered many-to-many.

Many-to-Many relationships cannot be created in Access.

Figure . Many-to-Many Relationship (Using a Junction Table)

In the above example, with a many-to-many relationship, a record in the

Employees table can have many matching records in the Project table,

and a record in the Projects table can have many matching records in

the Employees.

This type of relationship is only possible by defining a third table (called a

junction table) whose primary key consists of two fields the foreign keys

from both the Employees and Projects Tables.

A many-to-many relationship is really two one-to-many relationships with

a third table.


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What is QueryWhat is Query

An MS-Access query is a set of storedSQL instructions that manipulate and/orselect data from one or more tables.

SQL (Structured Query Language) is avery wi e y use ata ase anguagedesigned specifically for communicatingwith databases

SQL is not proprietary almost everyDBMS supports SQL (including MS-Access).


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What is QueryWhat is Query

Queries are extremely easy to set

up/use and provide an up-to-date

snapshot of your data at any time.

Queries may be used to calculate values

based upon existing fields, join fields

from separate tables, globally update ordelete data, and export linked/calculated

data to external programs.


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Types of QueryTypes of Query

Select Query

Update Querya e- a e uery

Append Query

Delete Query


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Select Query A Select Query extractdata from a table ( or from another

query) and present in desired / specifiedormat


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Make-Table Query Select data andcreates/populates new table.

Update Query Updates fields fromspecified table data

Append Query Runs query on onetable, appends results to another table

Delete Query Delete selected recordsfrom table


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Creating QueryCreating Query

Create Query Design Select

Table/Tables from Show table DialogSelect type of query


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QueryQuery Filtering DataFiltering Data

This query will return all records in the database for:Females

who are not white

whose height are greater than 150 cm

and who weigh between 60 and 70 kg


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QueryQuery Filter OperatorsFilter Operators

= equals

> greater than

>= greater than or equal

< less than


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Run a QueryRun a Query

Query Tools

Run Query


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Creating an Update QueryCreating an Update Query

Create a query with the necessary fields andselection criteria

Click the Update button in the Query Type

group on the Design tab. Access replaces theow an ort rows n t e es gn gr w t t e

Update To row

Click the Run button, and then click the Yes

button to confirm changing the records


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QueryQuery Calculating FieldsCalculating Fields

If there is ambiguity in the field names

between tables, you may need to type. .

Ex: emp.DA=30%*[emp.basic]


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Creating a MakeCreating a Make--Table QueryTable Query

Create a query with the necessary fields and selection

criteria

Click the Make Table button in the Query Type group

on the Design tab

In the Make Table dialo box, t e the new table name

in the Table Name list box. Make sure the Current

Database option button is selected to include the new

table in the current database, or click the Another

Database option button and enter the database name inthe File Name text box. Then click the OK button

Click the Run button, and then click the Yes button to

confirm the creation of the new table


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Creating an Append QueryCreating an Append Query

Create a query with the necessary fields and selection

criteria

Click the Append button in the Query Type group on

the Design tab

In the A end dialo box, select the table name in the

Table Name list box. Make sure the Current Database

option button is selected to include the new table in the

current database, or click the Another Database option

button and enter the database name in the File Nametext box. Then click the OK button. Access replaces the

Show row in the design grid with the Append To row

Click the Run button, and then click the Yes button to

confirm appending the records to the table


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Creating a Delete QueryCreating a Delete Query

Create a query with the necessary fields andselection criteria

click the Delete button in the Query Type

group on the Design tab. Access replaces theow an ort rows n t e es gn gr w t t e

Delete row

Click the Run button, and then click the Yes

button to confirm deleting the records


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SQLSQL

SQL (Structured Query Language) is avery widely used database languagedesigned specifically for

communicating with databases

SQL is not proprietary almost everyDBMS supports SQL (including MS-Access).]

SQL is a language that all commercialRDBMS implementations understand.


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SQL is relatively easy to learn, butextremely powerful one of theeasiest ways to learn is to use MS-Access Query by Examplemethods, then look at the

enerated SQL command

Remember that a query is nothingmore than the database engine

running the stored SQL command(it looks and sometimes acts like atable, but really adds little mass tothe database file)


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SQL supports various data types

Decimal numbers--- NUMBER, INTEGER .

Number is an oracle data type. Integer is an ANSI data type. Integer is

equivalent of NUMBER(38)

The syntax for NUMBER is NUMBER(P,S) p is the precision and s is

the scale.

Floating point numbers---- FLOATxe eng c arac er s r ngs---- en

Fixed length character data of length len bytes. This should be used

for fixed length data.

Variable length character strings --- Varchar2(len)

Variable length character string having maximum length len bytes. We

must specify the size

Dates-----DATE


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Operators

Arithmetic operators like +,-,*,/

Logical operators: AND, OR

Relational operators: =,=, < >

Retrieval Operator : Like, In, Between , Not NULL

SELECT * FROM EMPLOYEE WHERE SAL > 10000;

SELECT * FROM EMPLOYEE WHERE (SAL > 10000 AND

AGE > 25);SELECT * FROM SP WHERE QTY IS NOT NULL

SELECT * FROM P WHERE PNAME LIKE C*

SELECT SNO FROM S WHERE CITY IN (PARIS ,ROME)


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NULL

Missing/unknown/inapplicable data represented as a null value

NULL is not a data value. It is just an indicator that the value is

unknown


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SQL has three flavours of statements. The DDL, DML

and DCL.

DDL is Data Definition Language statements. Some examples:

CREATE - to create objects in the database

ALTER - alters the structure of the database

DROP - delete objects from the database

GRANT - gives user's access privileges to database

REVOKE - withdraw access privileges given with the GRANT

command


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DML is Data Manipulation Language statements. Some

examples:

SELECT - retrieve data from the a database

INSERT - insert data into a table

UPDATE - updates existing data within a table

DELETE - deletes all records from a table, the space for the records

remain


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DCL is Data Control Language statements.

Examples:

COMMIT - save work done

SAVEPOINT - identify a point in a transaction to which you can

later roll back

ROLLBACK - restore database to original since the last

COMMIT


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SQL - CREATE TABLE

Syntax:

CREATE TABLE tablename (column_name data_ type

constraints, )

Example:

CREATE TABLE Emp (

Job Char(10) UNIQUE,

Hiredate Date,Sal single,Comm single,

DeptNo REFERENCES DEPT(DeptNo));


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SQL - DROP TABLE

DROP TABLE TABLENAME

Deletes table structure

Cannot be recovered

Use with caution

DROP TABLE EMP;


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SQL - INSERT TABLE

Syntax: INSERT INTO tablename VALUES (value list)

INSERT INTO S VALUES(S3,SUP3,BLORE,10)


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SQL UPDATE TABLE

Syntax:

UPDATE tablename SET column_name =value [ WHERE

condition]

With or without WHERE clause

Examples:

UPDATE S SET CITY = KANPUR WHERE SNO=S1

UPDATE EMP SET SAL = 1.10 * SAL


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SQL - DELETE TABLE

With or without WHERE clause

Syntax: DELETE FROM tablename WHERE condition

=

DELETE FROM SP


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SQL SELECT TABLE

To select a particular column:

SELECT ColumnName FROM Tablename

To select set of column names,

SELECT column1, column2, FROM TableName

To select all columns from a table:

SELECT * FROM TableName

Examples:

Get the names of all the suppliers

SELECT SNAME FROM S;

Get the names and city of all the suppliers

SELECT SNAME, CITY FROM S

Get full details for all Suppliers in S table

SELECT * FROM S


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SQL - Aggregate functions

Used when information you want to extract from a table has to do

with the data in the entire table taken as a set.

Aggregate functions are used in place of column names in the

SELECT statement

The aggregate functions in SQL are :

SUM( ) , AVG( ) , MAX( ) , MIN( ), COUNT( )

SELECT SUM (QTY) FROM SP WHERE PNO=P2

SELECT AVG(QTY) FROM SP WHERE SNO=S1

SELECT MAX(QTY) FROM SP WHERE SNO =S1

SELECT COUNT(Qty) FROM SP WHERE PNO=P2

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Database Query and SQL