SQL Lion

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Here comes the real deal, sometimes you may face some unexpected things happening in SQL Server while creating SSIS package or dealing with the same, like missing Foreach File Enumerator or Foreach Item Enumerator in Foreach loop container. You might be thinking that, maybe it is not available in my piece of software.

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Optimizing Indexes in SQL Server: Although there are many bright faces of indexes but every coin have two sides. So it’s always advisable to implement indexes wisely on a table. Here we will check out different perspectives to view indexes on a given table.

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Types of indexes: We have basically two types of indexes in SQL Server.

• Clustered index:  It’s a type of index where the data itself is arranged at the indexed column i.e. we have the actual data at the leaf nodes. For example, in a science definition pocket book, every word is arranged alphabetically and the definition of the word is given along with it. Here there is no need to look up for the referencing page, as in case of other example like in a general book with indexes at the end of the book, contains page number along with the term or word which is then followed to get the information about the term.

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Indexing has become a critical buzzword in the arena of databases. Not only database users, but also all of us are using indexes in our daily life.  Got puzzled? Let me give you one scenario. Have you ever noticed how did a librarian arranges and orders all the books in the library? And when you are asking for a particular book, he immediately gives it to you within some couple of minutes without searching the whole library. This is possible because he has already indexed each book and categorized them according to the author and the publisher and again ordered all the books falling under same author and publisher in an alphabetical order of the title. So when you ask for a particular book, he just refers to the shelf belonging to the author and publisher of the book and the book is with you in no time.

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SQL Server 2005 has some unique features to deal with the Transaction system in the database world. It has some unique sets to take care of every possibility of transactions or types of transaction. Technically, it will give us discrete ways to isolate the transactions from occurrence of deadlocks or crashes.

Before going deeper to the Isolation level that SQL Server provides to distinguish types of transaction, let’s have a look on the definition of the TRANSACTION. What does transaction means in real world and in a database scenario?

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In my previous article named “Programming Foreach Loop Container – Enumerating Excel Files”, we discussed about enumerating Excel files in a folder and load data from each excel file to the destination by using Foreach File enumerator.

But there may be cases where we may have data in the form of sheets in a single excel file. For example, the total sales of study materials over different countries.

To load all the sheets from a single excel file in Foreach Loop Container, we have to use “Foreach ADO.NET Schema Rowset Enumerator”. This special enumerator is used to enumerate through schema information about a data source i.e. the schema information supported by the OLEDB provider. For example, to get list of tables, schemas, column information, constraints, etc from a database.

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Sometimes we were not aware of the contents of any object and we have to do certain tasks as many times as the no. of contents of that object. For example, a folder contains some text files with employee information data and we have to load all the text files data to our SQL server employee table. Here, we don’t know about the count of the source but we have to roll over every file. For this type of situation, SSIS have a unique container called “Foreach Loop Container” that will enumerate with each text file in the folder.

It can be used in some other cases too like enumerating each sheet of a excel file, or parsing each row of a table, enumerating each child node of a given tree, etc. In SQL server 2000 DTS package, it is bit difficult to loop over any task but fortunately SSIS has a special container to accomplish such tasks.

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While building an ETL package, sometimes we come across to repeat same types of tasks many times i.e. like to do certain task depending upon the number of students in the class, or any other condition, etc. So instead of developing same containers or tasks so many times, it’s always better to iterate it with certain parameters.

To resolve the above situation, SQL Server Integration Service (SSIS) comes with one special container called “For Loop Container“. This container has the same logic that a “For loop” keyword have in leading programming languages. It will iterate through all the tasks inside it till the condition satisfies. It acts as a repeating control flow. For each iteration of the loop, the For Loop container evaluates an expression that is specified and repeats its workflow until the expression evaluates to False.

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