6.10.09

Schema Names in Oracle database

Listing the schema names in Oracle database:

For retrieving the schema names from the oracle database, we need to use dba_objects table.

select * from dba_objects

The above query will retrieve all the objects from the table. Below are some of the high level information.
Owner: Schema name
Object Name: Name of the object
Object_ID : Unique ID generated by the oracle database.
Object_type : Type of the object whether its a table/index/view or synonym
Created : creation time
Valid : Whether this object is valid or not?


Below is the query used to fetch all the schemas located in the oracle database.

select owner,count(owner) cnt from dba_objects group by owner

It includes all the system related schemas. This can be removed by using not in operator. Schema names like Oracle, Common, system, xdb etc.., were related to Oracle system related schemas.

Thanks and Regards,

Venkatesan Prabu .J

Happy Learning!!!

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19.9.09

Bulk Insert option in sql server

Bulk insert is a very nice option in sql server to load huge data from the external source system.
It needs the data should be delimeted by specific delimeter.

The syntax is,

BULK INSERT TABLENAME
FROM SOURCE FILE
WITH (OPTIONS)

Now, I will create a temporary table to insert the records into the table.
create table testing
(
empname varchar(20),
value1 varchar(10)
)

Am having a text file with comma seperated delimeter and /n for the next line.



Now, am going to insert the data into the temporary table. Below is the bulk insert
syntax to insert the records into the table.

BULK INSERT testing
FROM 'C:\VP Personal\aa.txt'
WITH
(
FIELDTERMINATOR = ',',
ROWTERMINATOR = '\n'
)

On selecting the table, we will get the records inserted into the table.

select * from testing


Thanks and Regards,
Venkatesan Prabu .J

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SQL Server errors

While trying to use bulk insert option, I got the below error,

Msg 4861, Level 16, State 1, Line 1

Cannot bulk load because the file "\\ServerName\input\FileName.csv" could not be opened. Operating system error code 5(Access is denied.).

On digging the microsoft URL's I found the problem is due to the settings in sql server. We need to enable TCP/IP with local and remote connections option in Surface area configuration manager.

I have crossed this and next I got another peculiar error,
A transport-level error has occurred when sending the request to the server. (provider: Shared Memory Provider, error: 0 - No process is on the other

On looking into this issue, guessed the problem should be with the file. Some how, My sql doesn't have proper access to read that file. I took the file and placed it another location. Luckily, my problem is resolve and am able to do my bulk insert.

Any way, this is not a permanent and apt solution. For more proper solutions, please check the below URL.

http://blogs.msdn.com/sql_protocols/archive/2005/09/28/474698.aspx

Thanks and Regards,
Venkatesan Prabu . J
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9.9.09

Tempdb is full - Free up the space

Hi All,

Am writing my article after a very long time. I have been caught up with some other works.



Ok, lets see some interesting facts about tempdb.

Background of Tempdb Database:

TempDB is one of the system database which is used to store the temporary tables or temporary data.



A table can be declared as temp table by adding '#' symbol in the front of the table name.



Temp table will hold a session value appended, For each user a temp table can be created with a session id appended to its name - Unique to identify the tables. Internally, SQL Server will take care of this.


Actions for Tempdb full problem:


Considering, My scenario - Tempdb is full. In this case,



1. Check the feasibility to restart the server. If there is no major impact, restart the server. So that, the database will be freed up and it will more room to get other new tables.

Some times, we are familiar with the below error message.


Description: The LOG FILE FOR DATABASE 'tempdb' IS FULL.

Back up the TRANSACTION LOG FOR the DATABASE TO freeup SOME LOG SPACE

select * from sys.database_files

The above query will get the results as below,


Now, since the log file is full and there is no room to extend further. In that case, we

can advise the database to point the file to another location. Below is the query to achieve the same.


The file "templog" has been modified in the system catalog. The new path will be used the next time the database is started.




Cheers,

Venkatesan Prabu .J

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My T-SQL Gallery @code.msdn.microsoft


Created my own T-SQL Gallery in Microsoft site. Do visit the same and share your feedback,

http://code.msdn.microsoft.com/VenkatSQLSample/Thread/List.aspx

Thanks and Regards,
Venkatesan Prabu .J

SQL Server Interview questions - Part 1

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

What is SQL whats its uses and its component ?
The Structured Query Language (SQL) is foundation for all relational database systems. Most of the large-scale databases use the SQL to define all user and administrator interactions. It enable us to retrieve the data from based on our exact requirement. We will be given a flexibility to store the data in our own format.


The DML component of SQL comprises four basic statements:
* SELECT to get rows from tables
* UPDATE to update the rows of tables
* DELETE to remove rows from tables
* INSERT to add new rows to tables

What is DTS in SQL Server ?
Data Transformation Services is used to transfer the data from one source to our required destination. Considering am having some data in sql server and I need to transfer the data to Excel destination. Its highly possible with dialogue based tool called Data Transformation services. More customization can be achieved using SSIS. A specialized tool used to do such migration works.


What is the difference between SQL and Pl/Sql ?

Straight forward. SQL is a single statement to finish up our work.Considering, I need some data from a particular table. “Select * from table” will fetch the necessary information. Where as I need to do some row by row processing. In that case, we need to go for Procedural Logic / SQL.

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

Difference between primary key and Unique key?
Both constraints will share a common property called uniqueness. The data in the column should be unique. The basic difference is,
· Primary key won’t allow null value. Whereas, unique key will accept null value but only one null value.
· On creating primary key, it will automatically format the data inturn creates clustered index on the table. Whereas, this characteristics is not associated with unique key.
· Only one primary key can be created for the table. Any number of Unique key can be created for the table.

Select Statement in SQL Server

Select Statement in SQL Server

String Functions in sql server

String Functions in sql server
Substring/Len/replace/Ltrim/Rtrim

SQL Server Interview Question - Part 2

What is normalization?

Normalization is the basic concept used in designing a database. Its nothing but, an advise given to the database to have minimal repetition of data, highly structured, highly secured, easy to retrieve. In high level definition, the Process of organizing data into tables is referred to as normalization.


What is a stored procedure:
Stored procedures are precompiled T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. As, its precompiled statement, execution of Stored procedure is compatatively high when compared to an ordinary T-SQL statement.


What is the difference between UNION ALL Statement and UNION ?
The main difference between UNION ALL statement and UNION is UNION All statement is much faster than UNION,the reason behind this is that because UNION ALL statement does not look for duplicate rows, but on the other hand UNION statement does look for duplicate rows, whether or not they exist.

Example for Stored Procedure?
They are three kinds of stored procedures,1.System stored procedure – Start with sp_2. User defined stored procedure – SP created by the user.3. Extended stored procedure – SP used to invoke a process in the external systems.Example for system stored proceduresp_helpdb - Database and its propertiessp_who2 – Gives details about the current user connected to your system. sp_renamedb – Enable you to rename your database


What is a trigger?

Triggers are precompiled statements similar to Stored Procedure. It will automatically invoke for a particular operation. Triggers are basically used to implement business rules.


What is a view?
If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.


What is an Index?
When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index.


What are the types of indexes available with SQL Server?

There are basically two types of indexes that we use with the SQL ServerClustered -

1. It will format the entire table, inturn physically sort the table.

2. Only one clustered index can be created for a table.

3. Data will be located in the leaf level.

4. By default, primary key will create clustered index on the table.

Non-Clustered Index

1. It wont touch the structure of the table.

2. It forms an index table as reference to the exact data.

3. A reference to the data will be located in the leaf level.

4. For a table, we can create 249 non clustered index.

Happy Learning!!!
Regards,
Venkatesan Prabu .J

SQL Interview question

Extent Vs Page?

Pages are low level unit to store the exact data in sql server. Basically, the data will be stored in the mdf, ldf, ndf files. Inturn, pages are logical units available in sql server.The size of the page is 8KB.

Eight consecutive pages will form an extent 8 * 8KB = 64KB.

Thus I/O level operation will be happening at pages level.The pages will hold a template information at the start of each page (header of the page).

They are,

1. page number,

2. page type,

3. the amount of free space on the page,

4. the allocation unit ID of the object that owns the page.

Extents will be classifed into two types,

1. Uniform extents

2. Mixed extents

Uniform Extents:It occupied or used by a single object. Inturn, a single object will hold the entire 8 pages.Mixed

Extents:Mulitple objects will use the same extent. SQL Server will allow a max of eight objects to use a shared extent.

Property of SQL Server :Initally if an object is created, sql server will allocate the object to the mixed extent and once if the size reaches 8 pages and more... immediately, a new uniform extent will be provided for that particular object.

Herecomes, our fragmentation and reindexing concepts.



Best Joke - Enjoy it

Best Joke - Enjoy it