BIS05 Introduction to SQL

Business Information Systems Introduction to SQL Prithwis Mukerjee

Categories of SQL
Data Retrieval
Select
Data Manipulation Language (DML)
Insert
Delete
Update
Transaction Control
Commit
Rollback
Data Definition Language (DDL)
Create
Alter
Drop
Data Control
Grant
Revoke

Basics of Retrieval - 1 : Projection & Selection
Projection …. [ a subset of COLUMNS ]
Select Emp_ID, LastName, Salary from Employee
Select * from Employee
Selection … [ a subset of ROWS ]
Select * from Employee where Dept = ’40’

Basics of Retrieval – 2 : JOIN
Select EmpID, LastName, FirstName, Location from Employee, Department where Employee.Dept = Department.Dept_ID
JOIN

The Retrieval Process Select EmpID, LastName, FirstName, Location from Employee, Department where Employee.Dept = Department.Dept_ID SQL statement entered through a program Output returned to another program OR screen Actual Data stored in the RDBMS ‘engine’

Some ‘Select’ statements
Select * from Employees;
Select LastName, JobDesc from Employees ;
Select distinct JobDesc from Employees;

‘Where’ : to eliminate some rows
Select LastName, FirstName, JobDesc where JobDesc = ‘Clerk’;
Select LastName, FirstName, Salary where Salary > 35000;
Select LastName, Firstname where JobDesc <> ‘Clerk’;

Do you LIKE wildcards ?
Select LastName, FirstName, JobDesc from Employees where LastName like ‘D%';
Select LastName, FirstName, JobDesc from Employees where LastName like ‘_ _ _ _ i _’;
Select LastName, FirstName, JobDesc from Employees where LastName like ‘ _ _ _ _ i%’;

IN - BETWEEN
Select LastName, FirstName, JobDesc, Salary from Employees where Salary is between 10000 and 20000;
Select LastName, FirstName JobDesc, Dept from Employees where Dept in (’40’, ’20’, ’30’);

Order ! Order !!
Select LastName, FirstName, JobDesc, JoinDate from Employees ORDER BY JoinDate;
Select LastName, FirstName, JobDesc, Dept from Employees where Dept in (’20’,’30’,’40’) order by Dept;

More Restrictions : AND
Select LastName, FirstName, JobDesc, Salary, Dept from Employees where Dept = ’20’;
Select LastName, FirstName, JobDesc, Salary, Dept from Employees where Dept = ’20’ and Salary > 10000;
Select LastName, FirstName, JobDesc, Salary, Dept from Employees where Dept = ’20’ and Salary > 10000 and JobDesc = ‘Clerk’;
No rows returned !

Less Restrictions : OR
Select LastName, FirstName, JobDesc, JoinDate, Salary from Employees where JobDesc like ‘%Manager’ OR Salary >= 25000;
Select LastName, FirstName, JobDesc, JoinDate, Salary from Employees where JobDesc like ‘%Manager’ OR Salary >= 25000 OR FirstName = ‘Madhuri’

Matters of Precedence
Select LastName, FirstName, JobDesc, Salary where JobDesc = ‘Cus_Rep’ OR JobDesc = ‘Clerk’ AND Salary < 16000;
Select LastName, FirstName, JobDesc, Salary where (JobDesc = ‘Cus_Rep’ OR JobDesc = ‘Clerk’) and Salary < 16000;

Functions …
Two kinds of functions ….
Single row functions
Manipulate data items from one row
Accepts multiple arguments and return one value
Arguments can be column value or expression
Acts on one row
Returns one result per row
Can be nested
Multiple row functions
Works with data items from multiple rows
Arguments can be column value or expressions
Returns ONE result for a set of rows

Single Row Functions
Select EmpID, Salary, Comm, Salary+Comm*Salary from employee where DeptID = ’30’;
Select concat (‘Mr.’, Trunc(FirstName,1,1),’.’,LastName) from Employee where EmpID = ‘742866’;
Mr. A.Bacchan

Multiple Row Functions ..
Select sum(salary) from Employee;
Select avg(salary) from Employee;
Select max(salary) from Employee;
Other functions
Count
Min
And so on …

MultiRow Functions : Group By & Having
Select Dept, sum(salary) from Employee Group by Dept;
Select Dept, sum(salary) from Employee Group By Dept having Sum(salary) < 100000

Variety of Single Row Functions
Case manipulation
Lower
Upper
Character manipulation
Concat
Substr
Length
Lpad / Rpad
Etc
Number functions
Round
Trunc
Mod
Date Arithmetic
Months_Between
Next_Day
Add_Months
Data Type conversion
To_number
To_date
To_char
This is only an illustrative subset. There are many more each with its own syntax ….

Join : accessing data from two tables
Select EmpID, LastName, FirstName, Location from Employee, Department where Employee.Dept = Department.Dept_ID
What happens if we miss the JOIN condition ?

Cartesian Product
Let us work with a slightly simpler table …
Select FirstName, LastName, DepartName from Employee, Department;
We get the Cartesian Product
This can lead to an enormously large number of rows
The JOIN condition is very important

The Outer Join
The common join is the Inner join
Where we pull out rows from both tables that have something ( the join key value ) in common
But what if there are rows in one table that do not have the common value … we use Outer Join
The syntax for performing an outer join in SQL is database-dependent. For example, in Oracle, we will place an "(+)" in the WHERE clause on the other side of the table for which we want to include all the rows.

Outer Join
Select FirstName, JobDesc, Dept_Name from Employee, Department where Employee.Dept (+) = Department.Dept_Id;
Select FirstName, JobDesc, Dept_Name from Employee, Department where Employee.Dept = Department.Dept_Id (+) ;

Full Outer JOIN
Select FirstName, JobDesc, Dept_Name from Employee, Full Outer Join Department where Employee.Dept = Department.Dept_Id;

SubQuery : An Alternate to JOIN
Select FirstName, JobDesc from Employee where Dept IN (Select Dept_ID from Department);
Select FirstName, JobDesc from Employee, Department where Employee.Dept = Department.Dept_ID

SELF JOIN : Joining a Table to itself
Suppose we have this table where we have an additional column called Manager that stores Manager ID
There is one person who does not report to anyone else.
Everyone else reports to department manager.
Department managers report to Executive
We want to know who report to whom

Self join
Select w.FirstName, w.JobDesc, w.Dept , ’reports to’, m.FirstName,m.JobDesc,m.Dept from Employee w , Employee m where w.Manager = m.EmpID

Insert ..
Insert into Department (’50’,’Research’,’123456’,’Pune’)

Update ..
Update Department set Manager = ‘123456’ where Dept_ID = ’40’;

Delete ..
Delete from Department where DeptID = ’40’;

Create View
Create View myView as (
Select .....
any SQL query
simple or complex
that we have
learnt about so far ..
)
Select * from myView ;

BIS05 Introduction to SQL

by Prithwis Mukerjee on Oct 07, 2009

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BIS05 Introduction to SQL — Presentation Transcript