How easy or difficult to write dynamic SQL ? TIP#110

This is one of the challenge for most of the developer to write dynamic SQL. Generally we follow the approach of string concatenation.

This seems very easy but we need to cast the  parameters in VARCHAR and sometimes we stuck in single code.

I am sure this happened with all of us. 

Let’s understand first a straight forward way which we (most of  us) are  using.

In example I am using person table of Adventureworks database and it is just a simple query  which provide person row according to primary key.

Now the above query is OK but it can be write in much better way with one of the SQL server in build stored procedure which is sp_executeSQL. This is one of the best way which have certain advantage which will discuss in next tip. Now see how we can write above query in much better way

DECLARE @BusinessEntityID   INT
DECLARE @DynamicSQL NVARCHAR(200)
DECLARE @Parameters NVARCHAR(100)

SET @BusinessEntityID = 1
SET @Parameters =N’@ParameterBusinessEntityID INT’

SET @DynamicSQL = N’SELECT * FROM [Person].[Person] WHERE BusinessEntityId = @ParameterBusinessEntityID ‘
EXECUTE sp_executesql @DynamicSQL, @Parameters,  @ParameterBusinessEntityID =@BusinessEntityID

If you see above query, you will find we are not using any type conversion the statement is clear.

This is one of the best way to write dynamic query which is not only increase your statement’s readability but also increase performance of your query with certain amount.

Which we will discuss in next tip.

I hope now you are eager to use this and replace all your old fashion dynamic queries.

Please do post your feedback.

Enjoy !!!

RJ !!!

Merge statement- A simple way for DML TIP#105

When, I first saw this statement a Hindi proverb  come to my mind which is “1 teer 2 nishane” . The meaning of this proverb means a single bow which hit two different aim in one shot.

So let me explain “Merge” statement in more detail. With the help of this Merge statement we can do insert ,update and delete with a single statement.

Let’s understand this by an example. Suppose we have two tables Source and Target as shown in below figure

Now these tables will have some data so lets write query to insert some pre pop data

Now what we want follow things

1) if  employeeId of source and target tables are not matched and if employee name starts with “S” in the source table  then insert the value in target table.  (means insert Sunil & steve’s records from source to destination table)

2) If employeeId of source and target tables are matched then update the Employee name from source table to target table  (if any record matched then update the employee name which not the case with current data)

3) If employeeId of source and target tables are not matched and Employee name in target table starts with “S” then delete that row from target table. (So Sunidhi’s row will be deleted from target table)

Let’s write Merge Statement  for all the 3 above work.

 

Now you observed that there is one more statements which is written explicitly apart from the condition which is OUTPUT clause which helps us to determine what operation is performed.

When you run this you will get following output

Now see the actual data in both the table.

 

So, a simple merge statement is doing all 3 operations like update, insert ,delete.

I hope this tip will help you some where.

Enjoy !!

RJ!!!

It is OK its NULL only TIP #103

 

We always take NULL very lightly. Like if we are designing database then whether it is necessary or not we allow the data field to accept null.We think it will not affect anything.

Actually , at some point this is not always true.

According to Microsoft NULL is an Unknown value. It is not EMPTY & ZERO. It is just unknown.

Now according to my experience NULL is very sensitive and should be handle with care.

While we are designing the database and in a particular table if a field can not be null according to business rule then please don’t allow NULL in that field for data consistency.

For example if we have a StudentEnrollment table and in the StudentEnrollment table  we have reference of StudentId which is primary key of StudentId and that can not be NULL then please don’t make the field null able.

Let me share some more interesting facts

1) Two null value not equal :-  Let me explain it with an example

Suppose I have tblStudentSource table  which has different columns and a course column which have some null values  as shown below

Now see below snap where we are comparing the null value course column. You will find in below snap that there is no result while we have null value in course

2)  Use IS NULL or IS NOT NULL  to handle null able column:-  If a column is null and you want to show all the columns which are null then instead of comparing NULL value with column as shown in above figure use IS NULL as shown in below figure

In similar way if we want result which not have null course then we can write below query

3) Handle NULL carefully with IN clause

Let me explain with an example so we have 2 tables which are tblStudentSource (as shown in above (image 1) and another table which is tblCourse as shown in below figure

Now if you see we have course column in tblStudentSource table which has values similar to tblCourse’s course column and tblStudentSource’s course column contain some NULL values

Now suppose we wrote following statement and expecting that it will return all the course which are in tblCourse

Oh !! it is not returning any course. The reason behind it is NULL is not handled properly. Now to get desire result we have to write following statement

 

So , be always careful when your column has null values.

I hope the above points might help you somewhere.

Enjoy !!!

Keep learning & Keep Sharing !!

Thanks

RJ

A myth about view TIP #102

 

I don’t know why every interviewer’s favorite question “Can we insert record using View ?” If you say Yes/No the interviewer will roaming around like so Can you update record using View?  or Can you delete record using view ?

I  hope everyone who is reading this article will be aware of what is view and how to create it ?

If not then need not to worry

“View can be see as a virtual table based on SQL SERVER result or in other world it is a layer above actual data tables” Or we can say when you want to hide actual table then you create a view wrapper”

You can easily create a View with following syntax

“CREATE VIEW

AS

QUERY “

Let’s understand this by an example.

Suppose in I have a database with name “IndiandotnetDB” which has a  table “tblStudentSource”

Now I created a  view just for fetching records from tblStudentSource

 

CREATE VIEW StudentSourceView
AS
SELECT StudentId,
       FirstName,
       LastName,
       Course,
       Detail
FROM tblStudentSource
Go

Now you can fetch records directly from  View as shown in below

SELECT * FROM StudentSourceView

You will get all the records from tblStudentSourceView

Now the Question “ Can you Insert record from View ?“

So the answer is specific condition you can.

In our scenario we will write following command and execute so the record will be added

So you are clear that we can Insert records from View.

In similar fashion we can update the records as shown below figure

We will following SQL statement as showing in figure in which we are going to update record no 2004 as shown in above figure

As shown record 2004’s FirstValue is updated to value “Updated”

 

Now in similar way we can delete the record using View.

Although there are certain other factor due to which “Insert/update/delete” is possible.

like we have only simple schema.

I will describe this later with more detail like  scenario where  we can not Insert/Uppdate/delete using view.

Till than Enjoy !!!

 

Thanks

RJ

Bulk Copy Program (BCP)–A simple way to export data in a file TIP#101

Let’s consider a scenario where the end user require a CSV file of all the records in a table then BCP is one of the simplest way.

BCP stands for Bulk copy program. By the name you got the feeling of lots of data .

Although, there are various options & parameters available with BCP but here we will talk about simple one .

To understand it more clearly lets consider an example.

I have a database with name “IndiandotnetDB” and in this database I have a table with name tblStudentSource which having few records as shown in below figure

Now, the objective here is to export all the data which is in tblStudentSource table to a CSV file.

to achieve this we will use BCP command.  We are running BCP from command prompt as shown in below figure

Although there are various other options available with BCP command but for current post I choose simple one .

Now let me explain the command

BCP IndiandotnetDb.dbo.tblStudentSource OUT d:\File\output\sampleExport.csv –S . –T –c

so in above command “IndiandotnetDB” is my database

“dbo” is schema

“tblStudentSource” is  a table whose data need to be export

OUT – here out stands for export (export the table or query data)

“D:\File\output\” is folder where I want exported file

“sampleExport.csv” is file name which will be created by BCP and contains entire records after execution of BCP command

-S is stands for server I used “.” for localhost we can provide instance name as well

-T is for trusted connection (we can use – U for username – P for password)

-c is stands for character data type if you are not using this then you have to provide data type for each fields of output query result

Below is the output of the command which we run “ a sampleExport.csv file with all the records”

I hope this simple post will help you some where. I will share more details about BCP command in coming post.

Thanks

RJ!!

Good things should be appreciated–SQL sentry Plan Explorer TIP #95

Although , It is out of box but I would like to share here. I am very choosy in food. When my mother/wife cooked food and I didn’t like the taste then I explicitly said I didn’t like but when food taste was awesome then I didn’t say a word.

My mother taught me “You should appreciate every thing which is good.” Your single appreciation word do things

1. You yourself feel better

2. The person who did the good thing will be motivated to do more good things (in my case more tasty food wow )

This lesson of my mother is now one of the rule life.

So here I would like to say  one of the best tools I came across is “SQL Sentry plan Explorer”.   There are various great features of this tool but I would like to share few things which attract me more

1) It comes in two versions (Basic & professional ) .Basic version is absolutely free free free.

2) It makes SQL developer’s life easy. You can easily  cross check query plan easily.

see below snap.

You can also view logical read ,table scan and various other useful data

You can download this from http://www.sqlsentry.com/

Enjoy!!

RJ!!

Very useful SET XACT_ABORT TIP#94

 

SET XACT_ABORT is one of the hidden gem we can say. It is helpful in many ways.

Let me explain by an example suppose you are working on a stored procedure which is doing a complex data manipulation. You though this query will run with in 1 minute when you run it from .NET or other code , but some how it took quite long time and with in one minute .NET or the code from which you run the query raised a command timeout.

Or we can say you have applied transaction in stored procedure and calling from .NET code and you have mention the command timeout in .NET .The ADO.NET program raised a timeout but still your query is running in background.

Now in such situation sometimes it happened the transaction which is running in SQL SERVER will be open transaction. Which might be a cause of locking problem.

In such situation  XACT_ABORT option is helpful.

By default XACT_ABORT option is off you can on it by following statement

   SET XACT_ABORT ON;

Now when this statement is on and if you face same situation as mentioned above it will rollback entire batch.

Let me explain with below example

Suppose I wrote following statement “Notice here XACT ABORT is OFF”

Now , when I run the above statements I will get following result in result window

And in the message window we will get following result

What it means instead of the error at least 3 records are inserted but sometimes you require either all or no record commit in the table then let me enable the option XACT_ABORT ON in the query

Now let me re run the statements again. When I run the above statements I got following result in message tab there is no result tab.what is means ??

It means what ever inserted is roll backed when an error occurred in a statement. Although The above example is not the best example of XACT_Abort but it will help to understand how to use it.

 

I appreciate your inputs on this valuable topic.

Thanks

RJ!!!

Data Compression–A unique feature PART–II TIP #92

 

In last post TIP #91  we talked about  What is Data compression ? What are the  features ?  Now in this tip we will take implement the data compression with basic steps.

So lets follow the steps

1) Right click on the table on which you need to implement compression. You will get following menu just select manage compression as shown in below figure

2) Once you click on the above option you will get following screen.

3) Now you can choose compression type from dropdown of the row either Page or Row . You can calculate estimated space saving by selecting the compression type. as shown in below figure

a) Page compression (In the last column you will find requested compressed space)

b) Row Compression (in the last column you will find request compression space)

Now once you selected appropriate compression type you can click on Next button of the wizard you will get below screen

Now you can generate the script for this compression type. We can directly run the script on database itself if we are sure which with compression type.

Once we run the above command on database we are good to go and our table is compressed.

I hope this steps will help you to compress our database tables.

Enjoy compression !!

Rj !!

Data Compression– a unique feature of SQL Server TIP #91

A part from performance many times we faced challenges related to space  of our database. Sometimes our database is actually taking huge space and sometimes it our mistake due to which it took space.

It is worst condition when you are on a dedicated hosting or cloud hosting with limited space. In such case “Compression” is one of the best option.

This feature introduce in SQL SERVER 2008 onwards with Enterprise & Developer Edition.

By the name it is clear that it compress the data and provide more space on disk.

There are 2 options available in Data compression

Row level compression:–

 Row level compression primarily turns fixed-length data-types into variable data-types, thereby saving space. It also ignores zero and null values saving additional space. Because of this, more number of rows can be accommodated in a single data page.

Page level compression:-

Page level compression initially performs Row Level compression and adds two additional compression features – Prefix and Dictionary Compression. Page level compression offers better space saving than row level compression. Although the page level compression produce more space but obvious the CPU utilization is higher in page level compression. Overall we can say the page level compression is highly CPU consuming operation means it involves lot of  CPU efforts for compress & de compression. So choosing this option requires a high CPU & RAM configuration machine. Due to this feature it mostly used in data warehouse database where repeated values occurs. using this option with a table where lots of write operation occurs in day to day activity will be a bad idea.

Now we aware of data compression and its two options. Now lets discussed some of the major points before using this valuable feature

1) Data compression is SQL SERVER feature so we don’t need to do any tweak or rewrite our application code which is a good thing.

2) Compression is real time so again you don’t need to re run a maintenance job each time to compress the data.

3) As mention earlier you have to pay bit CPU cost for compression.

4) with Compression data files MDF files, ldf files and buffer cache size can be improve.

5) Compression not compress FILESTREAM data object which is obvious.

6) Although maintenance of compressed index is higher.

In next post I will show simple steps for implementing this best feature.

Enjoy !!!

Thanks

RJ!!!

Kill–use this weapon carefully in SQL SERVER . TIP #90

When we heard “Kill” then first impression of this word is very bad. We always scare with this word.

In real world we never want this action  from anyone but in SQL Server case it is very helpful and help us many times.

This feature we can use but very carefully. It is something like we have to kill a cruel giant not the common innocent person.

Lets understand this by an example.

Suppose we wrote a stored procedure or function and by mistake we wrote a condition which is never ending. We didn’t realize this and when we run the stored procedure/function the SQL Server hangs , system is slow and many other issues occur and our stored procedure which we run still running and laughing on us.

In such situation we have to kill that particular stored procedure execution statement which is cruel giant and eating the resources.

See below statement

WHILE 1=1
BEGIN
  SELECT ‘Infinite Loop’
END

It is never ending loop. and it is running on our SQL SERVER and will never stop.

Now first step is to Identify the process id for this statement for this we can use either sp_Who or sp_who2 which we discussed in TIP #82.

Now when we run it you will find on Database “IndiandotnetDB” we have a SPID 53 which is last statement on below image. This SPID 53 is reference of above while loop which we have to stop any ways.

Now we know SPID so we can stop or KILL  as shown below the syntax is very simple of KILL

KILL SPID

Now we are good to go.

Note: Please use this KILL statement very carefully.

I hope this tip will help you some where to KILL or stop SQL SERVER enemies.

Enjoy !!!

RJ!!!