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Archive for the ‘Stored Procedures’ Category

What are SQL Query Hints?

July 5, 2014 Leave a comment

SQL server usually selects the best query plan required to execute a T-SQL query. However, there might be cases where the plans selected are not the best. In such situations, you can use the query hints to suggest the best possible plan/method of executing a query. The Query hints can be applied on all operators in a query. These hints apply to SELECT, DELETE, INSERT, UPDATE and MERGE. You can use the Query hints in the OPTION clause after the query.

Few commonly used Query hints with examples are as below.

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Advantages and differences between CHAR and VARCHAR datatypes in SQL Server

April 25, 2014 1 comment

Everyone reading this must have come across these datatypes, but have you ever thought what are the differences and advantages between these two?

The obvious difference that comes to our mind is related to the length. Yes! You are right. The varchar supports variable length and Char supports fixed length. This is the main advantage varchar datatype. for example,  let us consider varchar(10) and char(10) . To store “GEEKEPISODE”, both the datatypes will use the complete length allocated and to store “GEEK”, CHAR datatype will use the complete 10 characters  allocated, but VARCHAR will use only 4.

From the above examples it might seem that VARCHAR is better than CHAR all the time. But remember, CHAR was included as a separate datatype because it has certain advantages over VARCHAR.

Understanding MERGE Transact SQL Statement

July 5, 2011 1 comment

By using “Merge”, you can perform insert, delete and update on a table in a single SQL statement. This helps in synchronizing the tables as well.

However while using merge there are several points that you need to keep in mind. Few

  • In a “Merge” statement, a “When Matched” clause with a search condition cannot appear after a ‘When Matched’ clause with no search condition.
  • A “Merge” statement must be terminated by a semi-colon (;).
  • An action of type ‘DELETE’ is not allowed in the ‘WHEN NOT MATCHED’ clause of a MERGE statement.
  • At least one of the three MATCHED clauses must be specified, but they can be specified in any order. A variable cannot be updated more than once in the same MATCHED clause.
  • Any insert, update, or delete actions specified on the target table by the MERGE statement are limited by any constraints defined on it, including any cascading referential integrity constraints.

Few examples of merge are as given below.

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The string function SOUNDEX() and its purpose in SQL.

April 25, 2011 Leave a comment

The Soundex code was developed to help negate the effects of all the spelling variations that can occur for similar sounding names ( Smith, Smithe, Smythe, etc.).  This way, users can index records based on a Soundex code based on the sound  and “not” by how it is spelled.

The Soundex system is not infallible – the surnames Gough and Goff sound the same (Goff), but a different code is formed for these two names.  Soundex can however be used to a great extent to get a desired result ( atleast closer to a desired result) This is a commonly used algorithm by many researchers.

In SQL a string function is available for this and is usually comes handy.  The function is

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what does NULLIF() do ? how is it different from ISNULL()?

October 7, 2010 3 comments

NULLIF( ) : Returns a null value if the two expressions specified in the function are equal.

The syntax used is

NULLIF ( expression1 ,expression2 )

If expression1 = expression2, then the function will return NULL.

ISNULL( ): The function replaces a null expressions with a specified value.

The syntax used is

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Set Nocount On – Hide the number of records affected by a query

October 7, 2010 Leave a comment

Often it might be necessary to hide the number of records affected by a query. It can be a simple select or insert  statement . Ususally, as soon as we execute a query a message pops up on the messages tab as shown below with the number of records affected.

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GUID (Globally Unique Identifier) in SQL Server

October 7, 2010 1 comment

The GUID (uniqueidentifier) data type is one of the most interesting data types available. uniqueidentifier column holds a GUI, a string of 32 random hexa-decimal characters (0-9, A-F) in blocks separated by hyphens.  A GUID will look like

5166AA1D-A18F-4D3C-A7CA-3F3CBF8CEE2B 

EDCF4B8A-4154-449B-972A-2224F8450BF1

CEA4C383-51FD-4B99-A67D-F5C34D5F1013     

5D9FDC84-632D-4450-B183-04CBBEE87DC6

GUIDs have both Pros and cons. GUIDs are pretty big in size and require 16 bytes of storage. This usually makes it slow during joins of large dataset.

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