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Venkatesan Prabu MCITP,MCAD,MCTS,CCNA. Worked as a ProjectLead(Senior .Net developer,SQL DBA). Now, Managing Director of KAASHIV INFO TECH, Chennai This Blog aims in serving the community in a better way. This blog is read by developers in 159 countries with average of 400 hits per day. Please post your valuable suggestions and hold my hand to serve the community. Lets make a new world with good thoughts and good minds....... This blog serves the SQL server community all over the world.

15.7.09

Difference between the dates group by id

Scenario:

I got a nice question in a forum on getting the difference between the created date and the updated date for a particular id. The complication is, we will have lot of records with that id. We need to group it.

Solution:

The solution is too simple,

drop table venkat
create table venkat(id int, date1 datetime,date2 datetime)
insert into venkat values(1,'1/2/2009','3/3/2009')
insert into venkat values(1,'2/2/2009','4/3/2009')
insert into venkat values(2,'2/2/2009','3/3/2009')
insert into venkat values(2,'2/2/2009','4/3/2009')
select * from venkat
select id,datediff(dd,min(date1),max(date2)) as datedifferenc from venkat group by id

Thanks and Regards,

Venkatesan Prabu .J

DateAdd function in SQL Server

drop table aa
create table aa(col1 datetime,col2 datetime)

I need to insert some records in the table. I need today’s date in the first column and tomorrow’s date in the second column. This can be achieved by using dateadd function.

Dateadd function:

Suppose, I need to add the date by 1 day. The syntax for this is,

Dateadd(dd,1,datecolumn)

The value 1 can be replaced with any number, based on your requirement.

insert into aa values(getdate(),dateadd(dd,1,getdate()))

If I want my previous date, we can use negative value as below.

insert into aa values(getdate(),dateadd(dd,-1,getdate()))

Dateadd function with year changes:

insert into aa values(getdate(),dateadd(yy,1,getdate()))

Similarly, we can proceed with date/hour/minutes and seconds.

Thanks and Regards,

Venkatesan Prabu .J

14.7.09

Data type error in SSIS with oracle database

SQL Server Intergration services (SSIS) with Oracle database:

Fortunately, I got a chance to work with oracle database migration using SSIS. Below is a peculiar behaviour of SQL Server Integration services. I have connected OLE DB source and connected to a table. Dragged and dropped OLE DB Destination, I need to created new table, clicked “New”.

The syntax for the table got created with a create statement,

CREATE TABLE SQLGenerated (
"Type_RATES_ID" NUMERIC(12),
"Type_RATES_VN" NUMERIC(12),
"_TYPE_ID" NUMERIC(12),
"_RATE_TYPE" VARCHAR(2),
"LENDING_RATE" NUMERIC (7,6),
"HEDGING_MARGIN" NUMERIC (7,6),
"PROFIT_MARGIN" NUMERIC (7,6),
"COMMISSION" NUMERIC (7,6),
"ESTABLISHMENT_COST" NUMERIC (24,8),
"RATE_PERIOD" NUMERIC(6),
"DATE_FIX" DATETIME,
"MOD_USER_ID" NUMERIC(12),
"MOD_TIMESTAMP" DATETIME,
"_ID" NUMERIC(12),
"TOTAL_RATE" NUMERIC (7,6),
"FIXED_AMOUNT" NUMERIC (24,8),
"_AMOUNT" NUMERIC (24,8),
"_TYPE_RATE_DIFF" NUMERIC (7,6),
"MATURITY_DATE" DATETIME,
"_SWITCH_FLAG" NUMERIC(1)
)

On pressing “OK” button, am getting the below error.

ORA-00902: invalid datatype (OraOLEDB)

To resolve this issue,
1. I went back to oracle database
2. Created a script for the source database.
3. Copied the content and pasted it into the create table window.
4. Now it’s working fine.

The problem is due to the data type,

create table OracleGenerated
(
Type_RATES_ID NUMBER(12) not null,
Type_RATES_VN NUMBER(12) not null,
_TYPE_ID NUMBER(12) not null,
_RATE_TYPE CHAR(2),
LENDING_RATE NUMBER(7,6),
HEDGING_MARGIN NUMBER(7,6),
PROFIT_MARGIN NUMBER(7,6),
COMMISSION NUMBER(7,6),
ESTABLISHMENT_COST NUMBER(24,8),
RATE_PERIOD NUMBER(6),
DATE_FIX DATE,
MOD_USER_ID NUMBER(12),
MOD_TIMESTAMP DATE,
_ID NUMBER(12) not null,
TOTAL_RATE NUMBER(7,6),
FIXED_AMOUNT NUMBER(24,8),
_AMOUNT NUMBER(24,8) default 0 not null,
_TYPE_RATE_DIFF NUMBER(7,6) default 0 not null,
MATURITY_DATE DATE,
_SWITCH_FLAG NUMBER(1) default 0,
)
The problem is due to the datatype “Datetime”. SQL Server is generating datetime but oracle is not supporting the same. In turn, we need to modify the data type to “date” type.

Thanks and Regards,
Venkatesan Prabu .J

Renaming SQL Server objects

Renaming SQL Server objects like table/Index/functions:

Renaming the object is a very challenging and interesting part in SQL Server.

Scenario: I have created a table and my boss is asking me to change the name of the table.
How can I achieve it? This can achieved using sp_rename

Let's see, how we are achieving it

Creating the table named Venkat with two column id and nam
create table Venkat(id int,nam varchar(10))
Am trying to create an index on the column id on the table venkat
create clustered index Venkat_Index on venkat(id )
--------------------------------------------------------------------

Renaming the index name on the table venkat
The syntax is,
exec sp_rename 'tablename.OldIndexID','new index name','index'
Example,
exec sp_rename 'venkat.venkat_index','Venkat_modified_index','index'
--------------------------------------------------------------------

Renaming the column name on the table venkat
The syntax is,
exec sp_rename 'tablename.OldColumnID','new Column name','column'
Example,
exec sp_rename 'venkat.id','id1','column'
--------------------------------------------------------------------

Renaming the name of the table
The syntax is,
exec sp_rename 'OldTableName','new Table Name'
Example,
exec sp_rename 'venkat','New_Venkat'

--------------------------------------------------------------------
While using this option, we used to get the below message from SQL Server
Caution: Changing any part of an object name could break scripts and stored procedures.
It indicates that the relative objects will get affected due to this change.
---------------------------------------------------------------------

Thanks and Regards,
Venkatesan Prabu .J

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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.

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.