Fixing SQL Server Error : The backup set holds a backup of database other than the existing database.

We faced this error while restoring a database in Sql Server using the .bak(backup)  file but into a different database.

The way it was resolved for us was to

1) Selecting Options within Restore Database dialog box.

2) Specifying correct path to the mdf and log file for the database.

3) Checking Overwrite the existing database option.

That’ s it ..

Changing authentication mode for Sql Server express edition

One way of doing it is through sql server management studio explained over here

http://msdn.microsoft.com/en-us/library/ms188670.aspx

But if you haven’t installed the management studio than in that case you need to make following change in the registry

HKEY_LOCAL_MACHINE / SOFTWARE / Microsoft / Microsoft SQL server / MSSQL.1/ MSSQLSERVER/ LoginMode

Click on it change it’s value from 1 to 2.

Then Restart your sql server service !!!

After you have done this you need to enable you sa account for sql server authentication for this follow these steps

1) Open SQL Server Management Studio Express and Login
2) In Object Explorer, click Security followed by Logins
3) Right click sa user and select Properties.
4) Uncheck Enforce password policy
5) Select Status. Click the Grant and Enabled radio buttons. Click OK
6) Restart your database server and select restart.

That’s it

Understanding Normalizations in Database(RDBMS)

Let’s try understanding normalization

How many normal forms are there?

There are seven normal forms.

They are

  • First Normal Form
  • Second Normal Form
  • Third Normal Form
  • Boyce-Codd Normal Form
  • Fourth Normal Form
  • Fifth Normal Form
  • Sixth or Domain-key Normal form

Why do we need to do normalization?

To eliminate redundancy of data i.e. having same information stored at multiple places, which eventually be difficult to maintain and will also increase the size of our database.

With normalization we will have tables with fewer columns which will make data retrieval and insert, update and delete operations more efficient.

What do we mean when we say a table is not in normalized form?

Let’s take an example to understand this,

Say I want to create a database which stores my friends name and their top three favorite artists.

This database would be quite a simple so initially I’ll be having only one table in it say friends table. Here FID is the primary key.

FID FNAME FavoriteArtist
1 Srihari Akon, The Corrs, Robbie Williams.
2 Arvind Enigma, Chicane, Shania Twain


This table is not in normal form why?

FavoriteArtist column is not atomic or doesn’t have scalar value i.e. it has having more that one value.

Let’s modify this table

FID FNAME FavoriteArtist1 FavoriteArtist2 FavoriteArtist3
1 Srihari Akon. The Corrs Robbie Williams.
2 Arvind Enigma Chicane Shania Twain

This table is also not in normal form why?

We have now changed our table and now each column has only one value!! (So what’s left?)

Because here we are having multiple columns with same kind of value.

I.e. repeating group of data or repeating columns.

So what we need to do to make it normal or at least bring it in First Normal Form?

  1. We’ll first break our single table into two.
  2. Each table should have information about only one entity so it would be nice if we store our friend’s information in one table and his favorite artists’ information in another

(For simplicity we are working with few columns but in real world scenario there could be column like friend’s phone no, email , address and favorites artists albums, awards received by them, country etc. So in that case having two different tables would make complete sense)

FID FNAME
1 Srihari
2 Arvind
FID Favorite Artist
1 Akon.
1 The Corrs
1 Robbie Williams
2 Enigma
2 Chicane
2 Shania Twain

FID foreign key in FavoriteArtist table which refers to FID in our Friends Table.

Now we can say that our table is in first normal form.

Remember For First Normal Form

Column values should be atomic, scalar or should be holding single value

No repetition of information or values in multiple columns.

So what does Second Normal Form means?

For second normal form our database should already be in first normal form and every non-key column must depend on entire primary key.

Here we can say that our Friend database was already in second normal form l.

Why?

Because we don’t have composite primary key in our friends and favorite artists table.

Composite primary keys are- primary keys made up of more than one column. But there is no such thing in our database.

But still let’s try to understand second normal form with another example

This is our new table

Gadgets Supplier Cost Supplier Address
Headphone Abaci 123$ New York
Mp3 Player Sagas 250$ California
Headphone Mayas 100$ London

In about table ITEM+SUPPLIER together form a composite primary key.
Let’s check for dependency

If I know gadget can I know the cost?

No same gadget is provided my different supplier at different rate.

If I know supplier can I know about the cost?

No because same supplier can provide me with different gadgets.

If I know both gadget and supplier can I know cost?

Yes than we can.

So cost is fully dependent (functionally dependent) on our composite primary key (Gadgets+Supplier)

Let’s start with another non-key column Supplier Address.

If I know gadget will I come to know about supplier address?

Obviously no.

If I know who the supplier is can I have it address?

Yes.

So here supplier is not completely dependent on (partial dependent) on our composite primary key (Gadgets+Supplier).

This table is surely not in Second Normal Form.

So what do we need to do to bring it in second normal form?
Here again we’ll break the table in two.

Gadgets Supplier Cost
Headphone Abaci 123$
Mp3 Player Sagas 250$
Headphone Mayas 100$
Supplier Supplier Address
Abaci New York
Sagas California
Mayas London

We now how to normalize till second normal form.

But let’s take a break over here and learn some definitions and terms.

Composite Key: -Composite key is a primary key composed of multiple columns.

Functional Dependency – When value of one column is dependent on another column.

So that if value of one column changes the value of other column changes as well.

e.g. Supplier Address is functionally dependent on supplier name. If supplier’s name is changed in a record we need to change the supplier address as well.

S.Supplier–àS.SupplierAddress

“In our s table supplier address column is functionally dependent on the supplier column”

Partial Functional DependencyA non-key column is dependent on some, but not all the columns in a composite primary key.

In our above example Supplier Address was partially dependent on our composite key columns (Gadgets+Supplier).

Transitive DependencyA transitive dependency is a type of functional dependency in which the value in a non-key column is determined by the value in another non-key column.

With these definitions in mind let’s move to Third Normal Form.

For a table in third normal form

  • It should already be in Second Normal Form.
  • There should be no transitive dependency, i.e. we shouldn’t have any non-key column depending on any other non-key column.

Again we need to make sure that the non-key columns depend upon the primary key and not on any other non-key column.

Album Artist No. of tracks Country
Come on over Shania Twain 11 Canada
History Michael Jackson 15 USA
Up Shania Twain 11 Canada
MCMXC A.D. Enigma 8 Spain
The cross of changes Enigma 10 Spain

Although the above table looks fine but still there is something in it because of which we will normalize it further.

Album is the primary key of the above table.

Artist and No. of tracks are functionally dependent on the Album(primary key).

But can we say the same of Country as well?

In the above table Country value is getting repeated because of artist.

So in our above table Country column is depended on Artist column which is a non-key column.

So we will move that information in another table and could save table from redundancy i.e. repeating values of Country column.

Album Artist No. of tracks
Come on over Shania Twain 11
History Michael Jackson 15
Up Shania Twain 11
MCMXC A.D. Enigma 8
The cross of changes Enigma 10
Artist Country
Shania Twain Canada
Michael Jackson USA
Enigma Spain

Normally this is considered enough and we don’t really go on applying the other normal forms.

Most of real-world application has databases which are in third normal forms.

Bye

References:-

Head First SQL,

Murach Sql for Sql server,

http://www.stuart.edu/courses/im510/database/2NF.htm

Understanding Relationship in Database (RDBMS)

There are three type of relationships

1) One to one

2) One to many

3) Many to many

Say we have table1 and table2

For one to one relationship, a record(row) in table1 will have at most one matching record or row in table2

I.e. it mustn’t have two matching records or no matching records in table2.

For one to many, a record in table1 can have more than one record in table2 but not vice versa

Let’s take an example,

Say we have a database which saves information about Guys and whom they are dating.

We have two tables in our database Guys and Girls

Guy id

Guy name

1

Andrew

2

Bob

3

Craig

Girl id

Girl name

1

Girl1

2

Girl2

3

Girl3

Here in above example Guy ID and Girl ID are primary keys of their respective table.

Say Andrew is dating Girl1, Bob – Girl2 and Craig is dating Girl3.

So we are having a one to one relationship over there.

So in this case we need to modify the Girls table to have a Guy id foreign key in it.

Girl id

Girl name

Guy id

1

Girl1

1

2

Girl2

2

3

Girl3

3

Now let say one guy has started dating more than one girl.

i.e. Andrew has started dating Girl1 and say a new Girl4

That takes us to one to many relationships from Guys to Girls table.

Now to accommodate this change we can modify our Girls table like this

Girl Id Girl Name Guy Id
1 Girl1 1
2 Girl2 2
3 Girl3 3
4 Girl4 1

Now say after few days, comes a time where girls have also started dating more than one boy i.e. many to many relationships

So the thing to do over here is to add another table which is called Junction Table, Associate Table or linking Table which will contain primary key columns of both girls and guys table.

Let see it with an example

Guy id

Guy name

1

Andrew

2

Bob

3

Craig

Girl id

Girl name

1

Girl1

2

Girl2

3

Girl3

Andrew is now dating Girl1 and Girl2 and

Now Girl3 has started dating Bob and Craig

so our junction table will look like this

Guy ID

Girl ID

1

1

1

2

2

2

2

3

3

3

It will contain primary key of both the Girls and Boys table.

Why do we need one to one relationship when we can easily accommodate the values in a single row?

For isolating some sensitive data. Employee table with its salary information stored in a separate table.

Putting large data in a separate table say a BLOB or Image type in which we are saving an image or document.

This type of relationship is typically used to improve performance.

And for our One to Many and Many to Many relationship, they help in maintenance.

If we had been storing multiple values in a column it would have been very difficult to query that table.

For e.g. say we have hobby column in our student table

And hobby has multiple values

Student ID Student Name Hobby
1 Sandra Swimming, Reading
2 Jans Swimming, Rowing

What would be select query to find student name having hobby as reading or update swimming with dancing. It would be too difficult to write such a query.

So if we have these values separated in another table we can easily query it.

Bye