SQL Presentation(V1)

8/10/2019 SQL Presentation(V1)

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To protect the confidential and proprietary information included in this material, it may notbe disclosed or provided to any third parties without the approval of Hewitt Associates LLC.

SQL - an overview by Sridharan


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Agenda1. SQL In tr od uc tio n

2. SQL St at em en ts

3. B as ic s yn tax

4. Sel ec t St at em en ts

5. D at a f r om M u lt ip l e Ta bl e

6. Set o per ato rs

7. SQL Fu nc tio n

8. SQL Su b q uer ies

9. SQL View s

1 0. In c l u d in g C o n s tr ai n t s

11. Q u es t io n s


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Introduction to SQL


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Introduction to SQL

SQL stands for Structured Query Language.

AIM : In this session you will learn how to use SQL to access and manipulate data in MySQL, SQL Server, MS Access,Oracle, Sybase, DB2, and other database systems.

What is SQL?SQL is a standard language for accessing and manipulating databases.

When a user wants to get some information from a database file, he can issue a query.

A query is a user request to retrieve data or information with a certain condition.SQL is a query language that allows user to specify the conditions. (instead of algorithms -http://csis.pace.edu/~wolf/CIS101/algorithms1/sld001.htm ).

Concept of SQLThe user specifies a certain condition.

The program will go through all the records in the database file and select those records that satisfy the condition.(searching).

Statistical information of the data.

The result of the query will then be stored in form of a table.


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SQL Statements


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SQL Statements

Select - Data Retrival

InsertUpdate

Delete - Data Manipulation

Merge

Create

Alter

Drop -

Data Definition LanguageRename

Truncate

Commit

RollBack - Transaction Control

Savepoint

Grant

Revoke - Data control Language


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SQL Syntax


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SQL Syntax


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SQL Syntax (contd..)


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Select statement


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Select Statement

1. The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SELECT ...... FROM ...... WHERE ......

1. Select Syntax

SELECT [ALL / DISTINCT] expr1 [AS col1 ], expr2 [AS col2 ] ;

FROM tablename WHERE condition


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Data from Multiple Table


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Data from Multiple Table

SQL provides a convenient operation to retrieve information from multiple tables.

This operation is called join.

The join operation will combine the tables into one large table with all possible combinations

(Math: Cartesian Product), and then it will filter the rows of this combined table to yield useful information.

field1

A

B

field2

1

2

3

field1 field2

AA

A

12

3

B

BB

1

23


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Data from Multiple Table (Contd..)

Types of Joins

Equijoin

To determine an employees department name, you compare the value in the department_ID column in the employees tablewith the department_id values in the departments tables. The relationship between the employees and departments tablesin an equijoin,that is ,values in the department id column on both must be equal .frequently, this type of join involves primaryand foreign key complements. ( Note : Equijoins are also called simple joins or inner joins.)

Non equijoin

A none equijoin is a join condition containing something other then an equality operator.


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Data from Multiple Table (Contd..)

Outer join

Missing rows can be returned If an outer join operator is used in the join condition .the operation is plus sign enclosedin parentheses(+), and it is placed on the side of the join that is deficient in information. This operator has the effect ofcreating one or more null rows, to which one or more rows from the nondeficient table can be joined.

Two types of outer join.

1. Right outer join

2. Left outer join

Self join

Sometimes you need to join a table itself. To find the name of each employees, you need to join the employees tableto itself. Or perform a self join. For example ,to find the name of sridhars manager ,you need to :

1. Find sridhar in the employees table by looking at the last name column.

2. Find the manager number for sridhar by looking at the manager_ID column .when sridhars manager is 101 .

3. Find the name of the manager with employee_ID 101 by looking at the last name column.

Narasimhan employee number is 101 .so Narasimhan is sridhars manager. In this process you look in the table twice.


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Set operators


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Set operators

The set operators

The set operators combine the results of two or more component queries into one result. Queries containing setoperators are called compound queries.

Types of operators

1. UNION

2. UNION ALL

3. INTERSECT4. MINUS


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Set operators (Contd..)


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Set operators (Contd..)

UNION

All distinct rows selected by either query

UNION ALL

All rows selected by either query. including all duplicates.

INTERSECT

All distinct rows selected by both queries.

MINUS

All distinct rows that are selected by the first select statement and that are not selected in the second select statement .


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Function


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SQL Function

Functions are a very powerful feature of SQL and can be used to do the following ;

1. Perform calculation on data

2. Modify individual data items

3. Manipulate output for groups of rows

4. Format dates and numbers for display

5. Convert column data types

6. SQL functions sometimes take arguments and always return a value.


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Two types of SQL Function

Function

Single row function Multiple-row function


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Single Row Function

These functions operate on single rowsand return one result per row.

Character

Number

Date

Conversion

Multi-Row Function

Functions can Manipulate groups ofRows.These functions are known asgroup functions.

Aggregate function


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Single Row Function

Character

Number

DateConversion

General


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Single Row Function

General Function

1. NVL

2. NVL2

3. NULLIF

4. COALSECE

5. CASE

6. DECODE

Character Function

Case Manipulation

1. UPPER

2. LOWER

3. INITCAP

Character Manipulation

1. CONCAT

2. SUBSTR3. LENTH

4. INSTR

5. LPAD | RPAD

6. TRIM


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Single Row Function

Number Function

1. ROUND

2. TRUNC

3. MOD

Date Function

1. MONTHS_BETWEEN

2. ADD_MONTHS

3. NEXT_DAY

4. LAST_DAY

5. ROUND

6. TRUNC


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Conversion Function

Data-TypeConversion

Implicit Data-TypeConversion

Explicit Data-TypeConversion


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Implicit Data-Type Conversion

FROM TO

VARCHAR2 OR CHAR NUMBER

VARCHAR2 OR CHAR DATE

NUMBER VARCHAR2

DATE VARCHAR2


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Explicit Data Type Conversion

CHARACTERNUMBER DATE


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Explicit Data Type Conversion (Continued)

Function Purpose

TO_CHAR Specifies the Langue in which month andday names and abbreviations arereturned.if this parameter is omitted,thisfunction uses the default date languages

for the session.TO_NUMBER Converts a character string containing

digits to a number in the format specifiedby the optional format model fmt.

TO_DATE Converts a character string representinga date to a date value according to theformat specified. If format is omitted, theformat is DD-MON-YY


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Multi-Row Function

Aggregate Functions: Aggregate functions operate against a collection of

values, but return a single value.

( Note: If used among many other expressions in the item list of a SELECTstatement, the SELECT must have a GROUP BY clause!)


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Aggregate Functions

Aggregate functions:Aggregate Row Description

AVG (column) Returns the average value of a column

COUNT (column)

Returns the number of rows (without a NULL value) of a column

COUNT (*) Returns the number of selected rows

COUNT (DISTINCT column) Returns the number of distinct results

MAX (column) Returns the highest value of a column

MIN (column) Returns the lowest value of a column

SUM (column) Returns the total sum of a column


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Subquery


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Subquery

Using a subquery to solve a problem

Who has a salary greater than kapil?

Main Query

Which employees have salaries greater than kapils salary?

Subquery

What is Kapils salary?


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Subquery (Contd..)

Types of subquery

Single-Row-Subquery

Main query

Subquery ----------> One row

Multiple Row Subquery

Main query Subquery --------> More than one row


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Views


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View (Contd..)

What is view?

You can present logical subset or combinations of data creating views of data. A view is logical table based ontable or another view. View contains no data of its own but is like a window through which data from tables can be viewed orchanged. The tables on which is a view is based are called base tables. The view is stored as a select statement in the datadictionary.

Why use views?To restrict data access.

To make complex query easy.

To provide data independence.

To present different views of the same data .


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View (Contd..)

Types of views:

1. Simple views2. Complex views

Simple views & Complex views

Feature Simple views Complex views

Number of tables. One One or More

Contains functions. No Yes

Contain groups of data. NO Yes

DML operations through a view. Yes Not always


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Constraints


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Constraints (Contd..)

What are constraints?

1. Constraints enforce rules at the table level.

2. Constraints prevent the deletion of a table if there are dependencies.

Types of constraints:1. NOT NULL

2. UNIQUE3. PRIMARY KEY

4. FORIGN KEY

5. CHECK


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Constraints (Contd..)

Data integrity constraints:

Constraint Description

NOT NULL Specifies that column value can not contain a null value.

UNIQUE Specifies a column or combination of columns whose value

must be unique for all rows in the table.

PRIMARY KEY Uniquely identifies each row of the table .

FOREIGN KEY Establishes and enforces a foreign key relationshipbetween the column and a column of the referenced table.

CHECK Specify a condition must be true.


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THANK YOU

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SQL Presentation(V1)