Sql notes, sql server,sql queries,introduction of SQL, Beginner in SQL

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Database
A database is the place of storage of the data in the form of tables
Data means information which is very useful. A database is also collection of 1 or more tables.
Table – a table is a collection of rows and columns.
CELL
CELL
Columns
A cell is an intersection of a row and a column
A column is also called as a field / attribute
A record is also called as a row / tuple.
A table is also called as an entity / relation.
Note :-
• If we install any of the database related software(s) – we can create our own database, we can
create our own tables and we can store the data inside it.
• When we install any database s/w(s) – a part of hard disk will be designated / reserved to
perform database related activities
• A database can also contain other database objects like views, indexes, stored procedures,
functions, triggers etc, apart from tables.
Some of the database software(s) we have are,
Oracle, SQL Server, DB2, Sybase, Informix, MySQL, MS – Access, Foxbase, FoxPro
Among the above database software – some of them are DBMS and some of them are RDBMS
The s/w which is widely used today is Oracle. The different versions of Oracle starting from the earliest
to the latest are – Oracle 2, Oracle 3, Oracle 4, Oracle 5, Oracle 6, Oracle 7, Oracle 8i, Oracle 9i, Oracle 10g,
CHAPTER 1
RDBMS ConceptsRDBMS ConceptsRDBMS ConceptsRDBMS Concepts

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and the latest to hit the market is Oracle 11g. here ‘i’ stands for Internet and ‘g’ stands for Grid / Grid
computing.
RELATIONSHIPS
A relationship is the association between any two tables which preserves data integrity.
Relationships
Master (
Parent )
Dept No. Dept Name Emp No.
Emp
Name
Dept No. Salary
Detail (
Child )
10 Accounting 101 A 10 20000
20 Research 102 B 10 300000
30 Sales 103 C 20 30000
Relationship helps to prevent the incorrect data in the child tables
Once the relationship is created, one table becomes master (or parent) and the other one becomes the
child ( or detail ).
Whatever we insert into the child should be present in the master, else the record will be rejected from
the child.
The master table contains the master data which will not change frequently.
The child table contains the transactional data which will change quite often.
DBMS & RDBMS
DBMS – stands for Database Management System
DBMS is a database s/w which allows us to store the data in the form of tables.
RDBMS – stands for Relational DBMS
RDBMS is also a database s/w which has facility to handle more data volume, good performance,
enhanced security features etc when compared against DBMS.
Any DBMS to qualify as a RDBMS should support the Codd rules / Codd laws
Ex for DBMS – FoxPro, FoxBase, Dbase
Ex for RDBMS – Oracle, Sybase, DB2, Teradata, SQL Server, MySQL
CONSTRAINTS
A constraint is a condition which restricts the invalid data in the table.
A constraint can be provided for a column of a table.

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Types of Constraints
NOT NULL
UNIQUE
Primary Key
Foreign Key
Check
NULL
→ NULL is nothing, it is neither zero nor blank space
→ It will not occupy any space in the memory
→ Two NULLS are never same in Oracle.
→ NULL represents unknown value
→ Any arithmetic operation we perform on NULL will result in NULL itself. For ex, 100000 + NULL
= NULL ; 100000 * NULL = NULL
NOT NULL
- NOT NULL will ensure atleast some value should be present in a column
UNIQUE
→ It will not allow any duplicates in a column
→ UNIQUE column can take multiple NULL (s)
Primary Key
→ It is the combination of NOT NULL and UNIQUE
→ Only one PK is allowed in a table
→ PK identifies a record uniquely in a table
→ Creation of PK is not mandatory, but it is highly recommended to create
Foreign Key
→ FK creates relationship between any two tables
→ FK is also called as referential integrity constraints
→ FK is created on the child table
→ FK can take both NULL and duplicate values
→ To create FK, the master table should have PK defined on the common column of the master table
→ We can have more than 1 FK in a given table
CHECK
It is used to provide additional validations as per the customer requirements.
Ex - 1) sal > 0
2) empnum should start with 1
3) commission should be between 1000 & 5000

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Check
(sal >
0)
PK NN PK NN FK NN Unique Unique
Dept
No.
Dept name
Emp
No.
Emp
Name
Dept
No.
Salary Ph No. Email
10 Accounting 101 A 10 200000 2222 a@gmail
20 Research 102 B 10 30000 - -
30 Sales 103 C 20 400000 3333 -
RELATIONSHIP NULL

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SQL – Structured Query Language
SQL – it is a language to talk to the database / to access the database
SQL – it is a language, whereas SQL server is a database.
To work on SQL , a DB software (RDBMS) is required.
SQL is not case sensitive
Username - Scott
Password – Tiger
Troubleshooting Oracle
Error 1
The account is locked
Steps to rectify the error
• Login as username – ‘system’ & password – ‘manager’ or ‘password – ‘tiger’
• SQL > show user ;
User is “SYSTEM”
SQL > alter user scott account unlock ;
User altered
SQL > exit ;
Error 2
TNS : protocol adapter error
How to troubleshoot this
Cause is “oracle service has not started”
How to go here,
Settings – Control Panel – Administrative Tools – Services
Sort the list
There is an “Oracle Service ORCL” & “start the service”
CHAPTER 2
SQLSQLSQLSQL –––– Structured Query LanguageStructured Query LanguageStructured Query LanguageStructured Query Language

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This query gives the list of tables.
* - selects all
This query gives the description of the table “department”.
The description of the table has column names, constraints, datatypes
This query gives the description of the table “department”

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The above query gives the description of the “employee” table. But we see that all the data is in different
lines which makes it very difficult to analyse.
So we use the following command to see the data in a more orderly fashion,
The “set linesize” command helps in increasing the line size , thus the data is arranged in a orderly
fashion.

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The above command “set pagesize 20” increases the page size, thus accommodating more number of
rows in a single page.
The above query gives the value of only these 3 columns from the table “employee”.

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‘where’ clause is used to restrict the number of records displayed. It gives only the records of the
specified condition.
Any string data should be enclosed within single quotes ( ‘ ‘ ) and the same becomes case sensitive.
Assignment
1) List the employees in dept 20
2) List the employees earning more than Rs 2500.
3) Display all salesmen

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Operators are classified into,
• Arithmetic Operators ( +, - , * , / )
• Relational Operators ( > , < , >= , <= , = , < > or != - not equals to )
• Logical Operators ( NOT, AND, OR )
• Special Operators ( IN , LIKE , BETWEEN , IS )
SPECIAL OPERATORS
1) IN – it is used for evaluating multiple values.
Ex – 1) List the employees in dept 10 & 20
CHAPTER 3
OPERATORSOPERATORSOPERATORSOPERATORS

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2) List all the clerks and analysts
We can provide upto 1000 values at the max
2) LIKE – used for pattern matching
% (percentage) - matches 0 or ‘n’ characters
_ (underscore) - matches exactly one character
Ex – 1) List all the employees whose name starts with ‘S’
Whenever we use % or _ , always ensure that it is preceded by the word ‘like’
2) List the employees whose name is having letter ‘L’ as 2nd character

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ASSIGNMENT
1) List the employees whose name is having atleast 2 L’s
2) List the employees whose name is having letter ‘E’ as the last but one character
3) List all the employees whose name is having letter ‘R’ in the 3rd position
In the above query, we give 2 underscores before R%.
4) List all the employees who are having exactly 5 characters in their jobs

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Here , in single quotes – we give 5 underscores.
5) List the employees whose name is having atleast 5 characters
Here, also in single quotes – we give 5 underscores ( _____ )
3) BETWEEN operator – used for searching based on range of values.
Ex – 1) List the employees whose salary is between 200 and 300
4) IS operator – it is used to compare nulls

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Ex – 1) List all the employees whose commission is null
ASSIGNMENT
1) List all the employees who don’t have a reporting manager
LOGICAL OPERATORS
1) List all the salesmen in dept 30
2) List all the salesmen in dept number 30 and having salary greater than 1500

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3) List all the employees whose name starts with ‘s’ or ‘a’
4) List all the employees except those who are working in dept 10 & 20.
5) List the employees whose name does not start with ‘S’

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6) List all the employees who are having reporting managers in dept 10
ASSIGNMENT
1) List the employees who are not working as managers and clerks in dept 10 and 20 with a salary in
the range of 1000 to 3000
2) List the employees whose salary not in the range of 1000 to 2000 in dept 10,20,30 except all salesmen

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3) List the department names which are having letter ‘O’ in their locations as well as their department
names
SORTING
It arranges the data either in ascending / descending order
Ascending – ASC / Descending – DESC
We can sort the data using ORDER BY
By default, the data is always arranged in ASC order
For ex – 1) Arrange all the employees by their salary

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2) Arrange all the employees by their salary in the descending order
3) Arrange ename, sal, job, empno and sort by descending order of salary

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In the above query we have – order by 2 – thus it arranges only the 2nd column ‘salary’ in the descending
order.
Thus to arrange the specific columns in order – we must have to specify the column number.
NOTE :- ORDER BY should be used always as the last statement in the SQL query.
Selecting DISTINCT VALUES
The above query arranges all the distinct values of department number.

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We have 5 GROUP functions,
1) Sum
2) Max
3) Min
4) Avg
5) Count
Sum – returns total value
Max – returns maximum value
Min – returns minimum value
Avg – returns average value
Count – returns number of records
Ex – 1) display the maximum salary, minimum salary and total salary from employee
To give aliases for the columns :-
CHAPTER 4
GROUP functions and GroupingGROUP functions and GroupingGROUP functions and GroupingGROUP functions and Grouping

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3) The below query gives the total number of employees
4) The below query gives the number of employees who have commission
5) List the number of employees in department 30
ASSIGMENT
1) Display the total salary in department 30
2) List the number of clerks in department 20
3) List the highest and lowest salary earned by salesmen

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GROUPING
It is the process of computing the aggregates by segregating based on one or more columns.
Grouping is done by using ‘group by’ clause.
For ex – 1) Display the total salary of all departments
2) Display the maximum of each job

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HAVING
‘Having’ is used to filter the grouped data.
‘Where’ is used to filter the non grouped data.
‘Having’ should be used after group by clause
‘Where’ should be used before group by clause
For ex – 1) Display job-wise highest salary only if the highest salary is more than Rs1500
2) Display job-wise highest salary only if the highest salary is more than 1500 excluding department
30. Sort the data based on highest salary in the ascending order.
RESTRICTIONS ON GROUPING
- we can select only the columns that are part of ‘group by’ statement
If we try selecting other columns, we will get an error as shown below,
The above query is an error because ‘job’ is there in the select query but not in the group by query.

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If it is enclosed in any of the group functions like sum(sal) etc – then it is not an error. But whatever
table is included in the select query must also be included in the group by query.
The above problem can be overcome with the following query as shown below,
The below query is also correct to rectify the above error,
Whatever is there in the select statement must be there in the group by statement. But, whatever is there
in the group by statement need not be present in the select statement. This is shown in the above two
corrected queries.
ASSIGNMENT
1) Display the department numbers along with the number of employees in it

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2) Display the department numbers which are having more than 4 employees in them
3) Display the maximum salary for each of the job excluding all the employees whose name ends with
‘S’
4) Display the department numbers which are having more than 9000 as their departmental total
salary

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Statements – they help us to create the table and insert the data.
There are 3 types of statements,
DDL – Data Definition Language – the various commands in DDL are :- Create, Drop, Truncate,
Alter, Rename
DML – Data Manipulation Language – the various commands in DML are :- Insert, Update,
Delete
TCL – Transaction Control Language – the various commands in TCL are :- Rollback, Commit,
Savepoint
CREATE – It creates the table.
Before we study the Create command, let us first study the some of the basic datatypes we use in SQL.
1) CHAR :-
It stores the fixed length character data.
It can store the alphanumeric data (i.e, numbers and characters).
NOTE :
To clear the screen, the command used is,
cl scr ;
if it is a large query and we cannot type it repeatedly, then type in – SQL > ed ;
when we type ed ; - we get the notepad – after making the necessary changes – then click on the ‘x’
i.e, the close button at the top right corner – then click on yes when a dialog box asking whether to
overwrite the file comes – after this it comes to the oracle screen – in the next line , enter ‘/ ‘ and hit
on enter button – another way of ending the query is by typing ‘ / ‘ in the next line of the query – this
indicates the end of the query.
CHAPTER 5
STATEMENTSSTATEMENTSSTATEMENTSSTATEMENTS

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2) VARCHAR
It stores the variable length character data
It can store alphanumeric data.
Difference between CHAR & VARCHAR
Let us consider an example as shown below to explain the difference.
Name char (6) ;
Here we are defining name which is of 6characters in length.
Now, let us store ‘Tom’ in the name field. Let us understand how the memory is allocated for this,
Blank Space
Reserved / Non-reusable memory
When we declare anything of type char, the memory is allocated as of the size given and its fixed length
– hence it cannot be altered.
Now, when we give tom, it allocates 6 bytes for name char – only the 1st 3bytes are used to store Tom –
the rest becomes waste as it is a blank space and it is reserved memory.
The length(name) = 6.
Name varchar (6) ;
Here we are defining name which is of 6characters in length.
Now, let us store ‘Tom’ in the name field. Let us understand how the memory is allocated for this,
Null
Re-usable memory
T O M - - -
T O M . . .

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When we declare anything of type varchar, the memory is allocated as shown above and it is variable
length
When we give tom, it allocates 6bytes for name varchar – only the 1st 3bytes are used to store tom – the
remaining 3 fields becomes null. As we know the property of null – null does not occupy any memory
space – thus the memory is not wasted here.
The length(name) = 3.
Another difference is : -
In char, maximum value we can store is 2000 characters
In varchar, maximum value we can store is 4000 characters.
3) NUMBER
- it stores numeric data.
For ex – 1) sal number(4) ;
Here the maximum possible value is 9999.
2) sal number (6, 2) ;
Here, 2 – scale (total number of decimal places)
6 – precision (total number of digits including decimal places)
Maximum value is 9999.99
sal number (4, 3) ;
maximum value is 9.999
sal number (2, 2)
maximum value is .99
4) DATE
- it stores date and time
- no need to specify any length for this type.
For ex, SQL > order_dt DATE ;
Date is always displayed in the default format :- dd – month – yy
5) BLOB
Stands for – Binary Large Object
It stores binary data (images, movies, music files) within the database. It stores upto 4GB.
6) CLOB
Stands for – Character Large Object
It stores plain character data like varchar field upto 4GB.
NOTE :-
varchar2 – from 10g, varchar & varchar2 are the same.
Earlier, varchar was supporting upto 2000 characters and varchar2 was supporting upto
4000 characters.

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Create the following tables
PRODUCTS
ProdID ( PK )
ProdName ( Not Null )
Qty ( Chk > 0 )
Description
ORDERS
ProdID ( FK from products )
OrderID ( PK )
Qty_sold ( chk > 0 )
Price
Order_Date
We can see that the table has been created.
Now, let us verify if the table has really been created and also the description of the table,
The new table products has been added to the database.

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Thus, we get the description of the table products.
The new table orders has been created. We can see from the above query how to reference a child table
to the parent table using the references keyword.
Thus we can verify that orders table has ben created and added to the database.

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Thus, we get the description of the orders table.
Creating a table from another table :-
Now, we will see how to create a table from another table – i.e, it duplicates all the records and the
characterstics of another table.
The SQL query for it is as follows,
Thus we can see that we have created another table temp from the table dept.
We can verify it as shown below,
Thus, we can see that the table temp has been created.
Thus, we can see that the table temp has copied the structure of the table dept. Here, we must observe
that temp copies all the columns, rows and NOT NULL constraints only from the table dept. It never
copies PK, FK, Check constraints.
Thus, when in the interview somebody asks you “I have a table which has about 1million records.
How do I duplicate it into another table without using Insert keyword and without inserting it
individually all the records into the duplicated table ?
Answer is - Use the above query of creating a table from another table and explain it.

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Thus, from the above query – we can see that all the records of the table dept has been copied into the
table temp.
TRUNCATE
It removes all the data permanently, but the structure of the table remains as it is.
Ex – SQL > TRUNCATE TABLE test ;
DROP
It removes both data and the structure of the table permanently from the database.
Ex – SQL > DROP TABLE test ;
Let us understand the difference between drop & truncate using the below shown example,
Let us create 2 tables Test1 and Test2 as shown above.

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The above shows the description of the table test1.
The above gives the description of the table Test2.
Now, let us use the Truncate query on Test1 and Drop query on Test2 and see the difference.
The above 3 queries show that – 1st query has the table test1 truncated.
2nd query – it shows no rows selected – thus only the records from the table has been removed. 3rd query
– it shows that the structure of the table is still present. Only the records will be removed.
Thus, this explains the truncate query.

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Thus from the above queries we can explain how drop works. 1st query – it drops the table. Thus – the
entire structure and records of the table are dropped.
2nd and 3rd query – since, there is no table – select & desc query for test2 will throw an error.
Thus, this explains the drop query.
Hence, we have seen the difference between drop & truncate query.
10g Recycle Bin
DROP
FLASHBACK
PURGE
The functionality of Recycle Bin was introduced in Oracle 10G version only. Thus even though the table
has been dropped, we can still restore it using flashback command or we can permanently remove it
using the purge command.
This concept of Recycle bin was not there in the earlier versions of Oracle.
RENAME
TABLE
RECYCLE
BIN
What to
do?
RESTORE IT
PERMANENTLY REMOVE

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It renames a table.
For ex, let us see the query of how we do this renaming a table.
In the above 3queries – we have created a table temp which copies table dept – we see the records of the
table temp – and also check if the table has really been created.
Now let us rename temp to temp23 as shown below,
The above query is used to rename a table.
Now let us verify the contents of the table and check if it has really been modified,
See next page,

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Thus the table has been renamed and its contents are verified.
ALTER
- this query alters / changes the structure of the table (i.e, - adding columns, removing columns,
renaming columns etc ).
Now let us alter the table products (which we have created earlier).
1) Let us add a new column ‘model_no’ to the table.
Thus, a new column has been added. Lets verify it with the query shown below,

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2) Now let us drop the column model_no from products.
Thus, the column has been dropped.
Thus, we can see from the description of the table – the column model_no has been dropped.
3) Let us rename the column qty to qty_available.
Let us verify if it has been renamed,
NOTE : SELECT is neither DML nor DDL. It does not belong to any group because it does not alter
anything, it just displays the data as required by the user.

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DML
INSERT
It inserts a record to a table.
Let us observe how it is done,
This is how we insert values into a table. All characters and alpha-numeric characters(ex – 10023sdf78)
must be enclosed in single quotes (‘ ‘ ) and each value must be separated by comma. Also we must be
careful in entering the data without violating the primary key, foreign key , unique constraints.
Now let us see the table in which the data in has been inserted,
Now, let us insert data into the table orders in which a foreign key is referencing primary key,
Here, we see that 1001 is the same prodid as of the earlier table. Sysdate – it displays the current date set
in the system .
Now, let us see the table,

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Another way of inserting data into the table is shown below,
Now, let us see the table,
UPDATE :-
It updates one or more records.
For ex – 1) Let us update salary by increasing it by Rs200 and also give commission of Rs100 where
empno = 7369.
Now, let us update the said record as shown below,

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Let us verify if the record has been updated,
Thus, the record(empno – 7369) has been updated.
2) Increase all salary by 10%
Let us verify it,

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DELETE
It deletes one / some / all the records.
Let us create a table test from table emp – and see how to delete 1 record and how to delete all records
from it,
Thus, we have created the table test.

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Thus 1 row, ‘miller’ has been deleted.
Thus, the deletion has been confirmed.
TCL
Any DML change on a table is not a permanent one.
We need to save the DML changes in order to make it permanent
We can also undo (ignore) the same DML changes on a table.
The DDL changes cannot be undone as they are implicitly saved.
ROLLBACK
It undoes the DML changes performed on a table.
Let us see in the below example how rollback works,
Let us delete the employee table. When we perform select operation on emp, we can see that all the rows
have been deleted.
We now perform the rollback operation,

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Now let us perform the select operation,
Thus performing the rollback operation, we can retrieve all the records which had been deleted.
COMMIT
It saves the DML changes permanently to the database.
Committing after rollback & vice versa will not have any effect
Let us explain the above statement with an example,

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We can see that commit has no effect after rollback operation.
Thus, from above – we can see that rollback has no effect after commit operation.
During an abnormal exit – i.e, shutdown or if the SQL window is closed by mouse click – then all the
DML’s will be rolled back automatically.

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During a normal exit – exit ; - all the DML’s will be auto-committed – and there will be no rollback.
Ex – 1) INSERT
UPDATE
ALTER
DELETE
ROLLBACK
When we perform the following operations in the same order for a table – then INSERT, UPDATE will
be committed – because ALTER is a DDL – and thus all the DML’s above it will also be committed –
because DDL operations cannot be undone.
Here – only DELETE will be rolled back because it’s a DML.
2) INSERT
UPDATE
DELETE
ROLLBACK
Here, all are rolled back.
SAVEPOINT :
It is like a pointer (break-point) till where a DML will be rolled back.
Ex :-
Insert …
Save point x ;
Update …
Delete ..
Rollback to x ;
…
…
Here, only DELETE & UPDATE are rolled back.
INSERT is neither rolled back nor committed.
Assignments
1) Create the following tables
a) Table name :- STUDENTS

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regno (PK)
name (NN)
semester
DOB
Phone
b) Table name :- BOOKS
bookno (PK)
bname
author
c) Table name :- LIBRARY
regno (FK from students)
bookno (FK from books)
DOI –date of issue
DOR – date of return
2) Insert 5 records to each of these tables
3) Differentiate between,
a) Delete and Truncate
b) Truncate and Drop
c) Char and Varchar
d) Drop and Delete
Delete and Truncate
a) Delete – deletes whichever records we want to delete from the table
Truncate – deletes all the records whether we want it or not
b) Delete – can be undone
Truncate – cannot be undone.
NOTE – The Primary Key created using more than 1 column is called as composite primary key.
Ex – alter table lib
Add primary key (regno, bookno, DOI) ;
CHAPTER 6
SUBSUBSUBSUB ---- QUERIESQUERIESQUERIESQUERIES

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A sub-query is also called as a nested query.
Syntax of a sub-query
Select …
From …
Where … ( select …
From …
Where …
)
OUTER QUERY INNER QUERY
Here, the inner query will be executed first.
The output of inner query is passed as input to the outer query.
To write a sub-query, atleast 1 common column should be existing between the tables.
For ex :-
1) List the employees working in ‘Research’ department.
2) List the department names that are having analysts
3) List the employees in Research and Sales department

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Assignment
1) List the department names which are having salesmen in it.
2) Display the employees whose location is having atleast one ‘O’ in it.

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3) List the department names that are having atleast 1 employee in it.
4) List the department names that are having atleast 4 employees in it
5) Display the department names which are having atleast 2clerks in it
6) Display the 2nd maximum salary
7) Display the 3rd maximum salary

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8) Display the 4th least salary
This method is not efficient to find the maximum and minimum salary. The limit is 32. This is not
efficient if you want to find the 100th maximum salary.
We can have upto 32 levels of sub-queries only.
9) List the department names that are having no employees at all

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Joins are used when we need to fetch the data from multiple tables
Types of JOIN(s)
Cartesian Join (product)
Inner (Equi) Join
Outer Join - Left Outer Join, Right Outer Join, Full Outer Join
Self Join
CARTESIAN JOIN
- It is based on Cartesian product theory.
Here, each and every record of the 1st table will combine with each and every record of the 2nd table.
If a table A is having 10 records & B is having 4 records – the Cartesian join will return 10*4 = 40 records.
For ex, let us consider the following query
Display employee name along with the department name
CHAPTER 7
JOINJOINJOINJOIN
Cartesian Product Theory in Mathematics states that :-
Let there be two sets – A {1, 2, 3} & B {4, 5}
Thus the Cartesian product (A*B) will be,
A * B = { (1,4), (1,5), (2,4), (2,5), (3,4), (3,5) }
Thus there are 6 sets – order of A is 3 & order of B is 2. Therefore, 2*3 = 6 is the Cartesian
product.

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From above – we can see that the above query returns 56 records – but we are expecting 14 records. This
is because each and every record of employee table will be combined with each & every record of
department table.
Thus, Cartesian join should not be used in real time scenarios.
The Cartesian join contains both correct and incorrect sets of data. We have to retain the correct ones &
eliminate the incorrect ones by using the inner join.
INNER JOIN
Inner join are also called as equijoins.
They return the matching records between the tables.

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In the real time scenarios, this is the most frequently used Join.
For ex, consider the query shown below,
Select A.ename, A.sal, B.dname
From emp A, dept B
Where A.deptno = B.deptno - JOIN condition
And A.sal > 2000 - FILTER condition
Order by A.sal ;
Let us see the output shown below,
JOIN condition is mandatory for removing the Cartesian output.
Let us consider the following 2 scenarios shown below,
Scenario 1
A
P Q R
B
P S T
C
P X Y
We want

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P Q S X
The SQL query will be,
Select A.P, A.Q, B.S, C.X
From A, B, C
Where A.P = B.P Number of joins = 2
And A.P = C.P
Scenario 2
A
P Q R
B
P Q S T
C
P X Y
We want
P Q R S X
The SQL query is ,
Select A.P, A.Q, A.R, B.S, C.X
From A, B, C
Where A.P = B.P
And A.Q = B.Q Number of Joins = 3
And A.P = C.P ;
If there are no common columns, then reject it saying that the two tables can be joined.
But there are some cases – where the 2 columns will be same but having different column names.
For ex – customerid & cid
Therefore, Number of JOINS = Number of tables - 1
Therefore, Number of JOINS = Number of common columns

55
Display employee name, his job, his dname and his location for all the managers living in New York
or Chicago
ANSI style JOINS
This was introduced from Oracle 9i.
It is another way of writing inner joins with a few modifications.
Thus we, can see the changes ,
In the 2nd line - ,(comma) has been replaced by the word ‘join’
In the 3rd line – ‘where’ has been replaced with ‘on’
Assignment
1) Display employee name and his department name for the employees whose name starts with ‘S’

56
OUTER JOIN
It returns both matching and non-matching records
Outer join = inner join + non-matching records
Non-matching records means data present in one table, but absent in another table w.r.to common
columns.
For ex, 40 is there in deptno of dept table, but not there in deptno of emp table.
Display all the department names irrespective of any employee working in it or not. If an employee is
working – display his name.
Using right join

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Using left join
Using full join
A B
10 6
3 3
7
3
A CJ B = 60records A IJ B = 3records(3 matching)
A LJ B = 10records (3matching + 7non matching of A)
A RJ B = 6records (3matching + 3non matching of B)
A FJ B = 13records (3matching of A & B + 7nonmatching of A + 3nonmatching of B)
Assignment
1) Display employee name and his department name for the employees whose name starts with ‘S’

58
2) Display employee name and his department name who is earning 1st maximum salary
SELF JOIN
Joining a table to itself is called self join
The FROM clause looks like this,
FROM emp A, emp B
Or
FROM emp A join emp B - ANSI style
For ex, - Display employee name along with their manager name
Now, let us see how this i.e the logic (the above query) works,

59
Now, when we give the above query – in Oracle – it starts matching the ‘mgr’ column of emp A with the
‘empno’ of emp b – we get two tables because in self join – a duplicate of the table required is created.
Now let us consider the first employee Scott – it starts the mgrid of Scott with the empno of all the
records in emp B – when two ids match, then the empno in emp B becomes the mgr of the empno in
emp A. Thus, we can see that – mgr id 102 is matching with empno 102 Blake in emp B. Therefore, Blake
is the manager of Scott.
Similarly we do the same for all the other records of emp A and thus find the employees and their
respective managers.
Display the employees who are getting the same salary
Co – related Queries :
→ They are special type of sub – queries
→ Here, both outer & inner queries are inter-dependent
→ For each & every record of outer query, the entire inner query will be executed
→ They work on the principles of both sub – queries & JOIN(s).
For ex, Display the employee who is earning the highest salary
Emp (A)
EmpNo Ename Mgr
101 Scott 102
102 Blake 103
103 King -
104 Smith 103
105 Jones 104
Emp (B)
EmpNo Ename Mgr
101 Scott 102
102 Blake 103
103 King -
104 Smith 103
105 Jones 104

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Thus, if an outer query column is being accessed inside the inner query, then that query is said to be co-
related.
Let us see the logic i.e, how we get the 1st max salary :-
Emp (A)
EmpNo Ename Sal
101 Scott 3000
102 Blake 4000
103 King 5000
104 Smith 2000
105 Jones 1000
Since co-related queries are a combination of Joins and sub-queries.
It follows the concept of Joins and creates multiple copies of the same table.
Then it takes 1st record i.e, - Blake – sal is 3000. It starts comparing with the sal in the emp table,
3000 = 3000 - count starts from 0 – thus, 0 = 0
3000 < 4000 – thus, 0 ! = 1
3000 < 5000 – thus, 0 ! = 2
3000 > 2000 – thus , 0! = 2
3000 > 1000 – thus, 0 ! = 2 if the condition becomes false, then the count increments by 1. Here
3000 is less than 4000 & 5000, thus 0 ! = 2. Thus , Blake does not have the highest salary.
Similarly, it does for the next records,
Blake – salary of 4000 – but 4000 < 5000 – thus, 0 ! = 1. This is also false.
King – salary of 5000 – it is greater than everything – thus, 0 = 0. Thus, King has the highest salary.
But the query doesn’t stop here, it checks for Smith & Jones as well.
Similarly, if we want to find the 2nd maximum salary,
Then in the query, change ‘0’ to ‘1’ & here, the logic is – it compares until it gets 1 = 1.
For 3rd maximum salary – change 0 to 2 and so on – here, the logic is – it compares until it gets 2 = 2.
For any highest, always put it as ‘0’ in the query.
If you want n(th) salary, pass (n-1).
In interview – this is a definite question. They will ask you what is co-related queries. And then
they’ll ask you find, 1st or max or 3rd maximum salary – after you write the query – they will ask you
to explain the logic as to how it gets the same – draw the table and explain it to them just as shown
above.
Emp (B)
EmpNo Ename Sal
101 Scott 3000
102 Blake 4000
103 King 5000
104 Smith 2000
105 Jones 1000

61
Assignment
1) Display the least salary from the employee table.
2) Display top 3 person’s salaries from the employee table.
3) Write a query to display bottom 3 salaries
4) Display 1st and 4th maximum salary

62
5) Display 1st, 4th & 6th highest salaries in a single query

63
Functions – it is a re-usable program that returns a value.
There are 2 types,
• Pre – defined
• User defined
Pre – defined
→ GROUP functions
→ CHARACTER functions
→ NUMERIC functions
→ DATE functions
→ SPECIAL functions
These are used both in SQL and PL/SQL. PL – Procedural Language (it’s a extension to SQL, can contain
IF statements, loops, exceptions, OOPs, etc .. )
User – defined
Used only in PL/SQL and we will not study it here.
We have already learnt about GROUP functions.
CHAPTER 8
FUNCTIONSFUNCTIONSFUNCTIONSFUNCTIONS

64
Now, let us study the various CHARACTER functions.
CHARACTER functions
a) Upper
b) Lower
c) Length
For ex :-
In the 1st query, we see something called as dual.
Dual – is a dummy table which is used for performing some independent operations which will not
depend on any of the existing tables.

65
For ex,
1)
This gives the system date.
2)
3)
We use dual – when the data is not present in any of the existing tables. Then we use dual.
Length – it returns the length of a given string.

66
For ex,
1)
2)
3) Display all the employees whose name & job is having exactly 5 characters
REPLACE
It replaces the old value with a new value in the given string.
For ex,

67
Here, a – is the old value to be replaced with p – which is the new value.
This query replaces all the names which has ‘A’ in it with ‘B’.
Let us see the output as shown below,

68
SUBSTR
This is called substring.
It extracts ‘n’ characters from x(th) position of a given string.
For ex,

69
Here , (job, ‘1’ , ‘3’) – means from job – extract from 1st position , 3 characters.
1) Display the employees whose job starts with ‘man’
2) Display the employees whose job ends with ‘man’

70
INSTR
This is also called as instring.
It returns position of a given character in a given string.
For ex,
Select instr (‘oracle’ , ‘a’ , 1 , 1) from dual ;
Given string
Character to be searched
Position from where the search should begin
Number of occurences
Display all the employees whose name is having ‘L’

71
List the employees whose job is having atleast 2 A’s in it
CONCAT
It concatenates any two values or columns.
It is represented by - ||
For ex,
NUMERIC FUNCTIONS
1) Mod :- it returns the remainder when 1 number is divided by the other.

72
Display the employees earning odd numbered salaries.
Round
It rounds off a given number to the nearest decimal place.
Trunc
It truncates the given number to the given decimal place. Truncate does not do any rounding.
For ex,
Here, ‘1’ indicates the number of positions.
DATE FUNCTIONS
1) Sysdate
Stands for System date.
It returns both date & time, but by default – only date is displayed.
The default format is,
dd – mon – yy
2) Systimestamp
Introduced from Oracle 9i
Returns date, time and timezone.

73
Here, .914000 – gives the fraction of millisecond which keeps changing as shown below,
In interview – if they ask you – “ which function contains fractions of a second “ OR “how to see the
system time “ – then answer is “SYSTIMESTAMP”.
SPECIAL FUNCTIONS
1) TO – CHAR
Used for displaying the date in different formats.
For ex,

74
Now, let us see how to add 5 hrs to the existing time,
We can see that 5 hrs has been added to the current time.

75
NVL
It substitutes a value for a null.
For ex,
The above query means – if the employee has commission, then add sal + comm. To get total salary –
else add 0 to the sal and display total salary.
DECODE
It works like ‘if – then – else’ statement.
For ex,

76
The above query states that – in job, if clerk is there, replace with C – else if salesman is there, replace it
with S – else replace with ‘O’.
Display employee name, job, salary and commission. If the commission is NULL, then display -100
Display all employees whose name is having exactly 1 ‘L’ in it

77
Normalization is the process of splitting the bigger table into many small tables without changing its
functionality.
It is generally carried out during the design phase of SDLC.
Advantages
1) it reduces the redundancy (unnecessary repeatation of data)
2) avoids problem due to delete anamoly (inconsistency)
Normalization is a step-by-step process and in each step, we have to perform some activities.
STEPS IN NORMALIZATION
1) 1NF – 1st Normal form
2) 2NF – 2nd Normal form
3) 3NF – 3rd Normal form
1NF
- We should collect all the required attributes into 1 or more bigger entities.
- We have to assume no 2 records are same (i.e, records should not be duplicated)
CHAPTER 9
NORMALIZATIONNORMALIZATIONNORMALIZATIONNORMALIZATION

78
- Identify the probable primary key
At the end of 1NF, our data looks like this,
COLLEGE
RegNo - PK
Sname
Semester
DOB
MailID
Phone
BookNo - PK
Bname
Author
DOI
DOR
Fine
2NF
To perform 2NF,
- The tables have to be in 1NF
- Here, we identify all the complete dependencies and move them separately into different tables.
At the end of 2NF, our data looks like this,
STUDENTS BOOKS
RegNo - PK BookNo - PK
Sname RegNo - FK
Semester Bname
DOB Author
MailID DOI
Phone DOR
Fine
3NF
The table will have to be in 2NF
Here, we identify all the partial dependencies and move such columns to a separate table.
STUDENTS BOOKS LIBRARY
RegNo - PK BookNo - PK BookNo - FK
Sname Bname RegNo - FK
Semester Author DOI
DOB DOR
MailID Fine

79
Phone
Disadvantage of Normalization
The only minor disadvantage is we may have to write complex queries as we have more number of
tables to be accessed.
Denormalization is the process of combining more than 1 smaller table to form 1 bigger table is called as
denormalization.
CODD rules ( Differentiates between DBMS & RDBMS )
1) should support NULL values
2) should support creation of relationship between tables
3) should support DDL, DML, TCL
4) should support constraints like PK, Unique, CHK
5) should support query techniques like sub – queries, joins, grouping etc.
Oracle 9i Features (i means internet)
- TIMESTAMP datatype
- SYSTIMESTAMP function
- ANSI style joins
- Renaming a column
Oracle 10g features (g means grid)
- Recycle Bin
ERD - Entity Relationship Diagram
It is the pictorial representation of all the entities and their relationships (tables).
STUDENTS _
INTERNALS
RegNo - FK
Sid
Marks
STUDENTS
RegNo - PK
Sname
Semester
DOB
MailID
Phone
BOOKS

80
***** THE END *****
BookNo - PK
BName
Author
LIBRARY
BookNo - FK
RegNo - FK
DOI
DOR
Fine

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