Natural Join

In this lesson we are going to study about Natural Join in a database.

Natural Join:

• This join is having a special features ,with the use of this join no need to specify the join condition explicitly.
• This type of join offer a further specification of equi join .
• We have to specify the keyword Natural join in the join statement.
• Natural Join automatically joins two table based on columns in the two table which have same datatype and names.

Example: EMPLOYEE table and DEPARTMENTtable have a same column DepeartmentID and same datatype.
so we can join this two table using
NATURAL JOIN.



SQL :

SELECT *

FROM employee

NATURAL JOIN department;

Note:

• If we write a where clause of a select statement with two or more table then the order parser will start the join operation from right to left.In this case the table name which is written last will be processed,
•  The  join can happen only on columns having the same names and same data types in both the table .If the columns have the same name ,but different data types,then the NATURAL JOIN syntex causes an error.

Related Article

• Join
• Cross Join
• Equi Join
• Non  Equi Join
• Self Join 
• Join with Using clause.
• Join with ON clause
• Outer Join. 

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Self Join

In this lesson we are going to study about Self joins in a database.

Self Join: 

• In order to join a table to itself we use the self join.
• This type of join is used to compare values between two columns in the same table .

Example:-To find the name of Abhishek and Aritra manager we need to

1. find in EMPLOYEE table by looking the Emp_name columns.
2. find the manager number from Manager_id.
3. find the name of manager with manager_id.

sql query :-

select

      emp.Emp_Name as Employee_name,

      manager.Emp_Name as manager_name

from  employees emp,

      employees manager

where emp.manager_id=manager.emp_id

OUTPUT: 

In simulate two table in the from clause there are two  aliases ,namely emp and manager for the same table ,EMPLOYEE.



Related Article

• Join
• Cross Join
• Equi Join
• Non  Equi Join
• Natural Join 
• Join with Using clause.
• Join with ON clause 
• Outer Join

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Non Equi joins

In this lesson we are going to study about Non Equi joins in a database.
Non Equi Join:

Non eque join is a type of join in which we can join two table with the join condition where the join condition uses other than equal operator “=”.

Example: In the below diagram we are having two table EMPLOYEES and JOB_GRADES.

 EMPLOYEES tabel contain the lastname and salary of the employee and JOB_GRADE contain the grading (Gra),lowest salary and highest salary.

A relation between the two table is that the salary columns in the EMPLOYEES table must be between the values in the Lowest_sal and Highest_sal columns of the JOB_GRADES table.The relationship is obtained using an operator other than equal(=).

Non Equi join Sample:

select e.last_name,e.salary,j.gra

from employees e,job_grades j

where e.salary between j.lowest_sal and j.highest_sal

NOTE: Other condition ,such as <= and >= can be used ,but BETWEEN is the simplest .Remember specify the low value first and hight value last when useing BETWEEN.
Table aliases used for reduce the code length and as well as the execution time .

Related Article

• Join
• Cross Join
• Equi Join
• Self Join
• Natural Join 
• Join with Using clause.
• Join with ON clause
• Outer Join. 

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Equi Join

In this lesson we are going to study about Equi joins in a database.

Equi Join or Theta Join: 

• An Equi Join is a type of joins the tables based on the columns in two table with same values.
• In Equi join ,the join condition must have an Equility operator.
• Using other comparison operators (such as <) disqualifies a join as an equi-join.

Example: In the below diagram we are having two Table,Table:A and Table:B. In Table:A we are having five records and Table:B is having four

 records which is also in Table:A  if  we do the Equi join on Table:A column X with Table:B column Y,

 this will retrun the record which are common in both the table A column X and Table:B column Y .

NOTE:   The columns X of Table A and columns Y of Table B Datatype must be same and the resulting table is having all the columns of Table:A ,and Table:B.

Syntex:

Explicit Equi join:

SELECT *

FROM Table1

JOIN Table2 ON  Table1.columnX=  Table2. columnY ;

Implicit Equi join:

SELECT * FROM  Table1 ,  Table2  WHERE  Table1.columnX=  Table2. columnY ;

just have a look on below video and try to Cross Join table by your self and you can download the sql scrpit used in this video from here DOWNLOAD LINK

Related Article

• Join
• Cross Join
• Non  Equi Join
• Self Join 
• Natural Join  
• Join with Using clause.
• Join with ON clause
• Outer Join. (comming soon.)

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Cross join

In this lesson we are going to study about Corss joins in a database.
Cross Join  or Cartesian Product:

• Each row from the first table is combined with the each rows from the second table.
• Rows in the result table is the product of rows in each table.
• For large no of rows ,it takes longer time.
• It does not include any join condition .
• A Cross Join B Result table as  A*B.

Example1:In the below diagram we are having two table's Table:A,Table:B .Table:A is having one column X

with three data and Table:B is having one column Y with two data.So the value of  m=3 and n=2.
So when we are doing cross join of Table:A with Table:B this will return a table which have
m*n =3*2
       =6(Record)
i.e each row of one table is mapped with each row of second table.




Example2:  In the below diagram we are having two table's Table:R,Table:S .Table:A is having Two column A,column B

with three data and Table:S is having two column B.column C with two data.So the value of  m=3 and n=2.
So when we are doing cross join of Table:A with Table:B this will return a table which have
m*n =3*2
       =6(Record)
NOTE: Result table is having all columns of Table:R,Table:S

Syntax:
Explicit cross join:

SELECT *

FROM Table1
CROSS JOIN Table2



Implicit cross join:

SELECT *
FROM  Table1 , Table2;

just have a look on below video and try to Cross Join table by your self and you can download the sql scrpit used in this video from here DOWNLOAD LINK

 Related Article

• Join
• Equi Join
• Non  Equi Join
• Self Join 
• Natural Join  
• Join with Using clause.
• Join with ON clause
• Outer Join.  

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Joins

In this lesson we are going to study about joins in a database . In order to join rows from multiple table or view we use join in our statement in this session we will briefly discussing the join and type of join in database .
JOINS:

• Joins query are written in the where clause of the select statement.
• Joins condition :comparing two columns of two tables.
• Database engine joins the table according to the join condition .
• If we want to join more then two table then database engine evaluates columns of the two tables and then it joins the result to the other table.

Have a look this image which shows the operation of the join.

Table A and Table B is having some common columns .by giving the condition in where clause we can have the result of joined table.

NOTE: The columns which are using in join condition must have the same datatype . otherwise it will give error and to prevent this cause if having different datatype but still we want to use that columns in join condition then use the cast function to convert the datatype and then use in join condition .

Type of Joins:

 Joins are classified according to the different type way the join operation performed on the tables.

we will discuss about all this Join in details in the next section .
Related Article

• Cross Join 
• Equi Join
• Non  Equi Join
• Self Join 
• Natural Join 
• Join with Using clause.
• Join with ON clause
• Outer Join.  

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How To Attach mdf file in sql server

In the previous lesson we have already discuss about how to log in your database server and access your database  located in local server or remote server and all if you miss those lesson then just have a look here..

This article will assist with moving SQL Server Data File(s) (.mdf) and Log File(s) (.ldf) from one location to another using the attach and detach .but before going into step for attach and detach the mdf and ldf let talk in short about

what is mdf?

what is ldf?

what is ndf?

SQL Server databases have three types of files:

Primary data files:The primary data file is the starting point of the database and points to the other files in the database. Every database has one primary data file. The recommended file name extension for primary data files is .mdf.

Secondary data files:Secondary data files comprise all of the data files other than the primary data file. Some databases may not have any secondary data files, while others have multiple secondary data files. The recommended file name extension for secondary data files is .ndf.

Log files:Log files hold all of the log information used to recover the database. There must be at least one log file for each database, although there can be more than one. The recommended file name extension for log files is .ldf.

step to attach database file:

Step1:Just folllow the below screen and brose the attach file window.Right click on database >>all task>>attach database.

Step2:click on browse option in newer version this option named as add new  then select .mdf file and click on OK.

Step3: Now the database .mdf file is in browse window for confirmation click on OK other choss another .mdf file. After click on OK it will give message whether the file is attach or not.

step to detach database file: first select your database then give right click and select the detach option .
 step to move database file:  To move the database file there are two way first way is Stop the sql server and then go to the physical path of .mdf file copy and past it another place or in your hard disk and attach in other sql server  and remeber dont forget to start the sql server once you stop it .Second way is detach the database then copy the database and move it another location then again attach the database .mdf file.
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