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Learning By Sample -

T-SQL : Part 5

Learning By Sample Series

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Learning By Sample - T-SQL : Part 5

Foreword

Learning By Sample ?

So, why should I made this tutorial freely accessed by everyone ? Well, surely I am just nobody, I

also just another ordinary person with ordinary knowledge. However, I always feel that some persons in

the internet giving away their tutorial for free and I feel being helped by them. Then, I remember one of

my senior wisdom words : “If you want to be given more, then start to give more”. And of course, I really

believe those words, since that I already proof it to be right all the time.

Also, I’m not an English native speaker, however, I just try to improve my English in any other

way, especially in written format. Thus, I think writing is the best practice to improve my English freely.

However, you will find many grammatical errors in my tutorial, so please send me comments and also

suggestion to improve it.

Then, why the format using Learning By Sample series ? Is it really different with other tutorials

out there ? Ehm, I already wrote three books (in Indonesian) using this kind of format, and many readers

already contact me about how this format really help them to learn from the scratch. So, why in the

world I’m not re-create it in English format, right ? Eventhough actually, it is similar with Hands On Lab

series which already famous in Microsoft site previously.

All of my lesson also being designed as short samples and short time exercise. Thus, I hope that

each of tutorial series would take only at least 10-15 minutes maximum to learn. Why keep it short ?

Because many beginner (and even expert) will find boring whenever they must keep studying more than

15 minutes (but you will never get bored when you online in such time right ?).

Another reason is just because many of samples in this series come up from my lecturing task

exercise. So, I just try to compile all my lab exercises in order to keep it tidy and also reusable for my

students. That’s why you will find many unsorted course material inside these series, however, just take

a seat and enjoy the ride !

Requirements

So, what will you need before starting this simple tutorial ? First, you need a PC/laptop/netbook

which use at least Windows XP/Vista/Seven/Server as its operating system. And, you should also install

SQL Server (at least Express Edition) from version 2005 and above. And remember, if you have SQL

Server Express Edition, make sure that you already download and install its SQL Server Management

Studio too.

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Learning By Sample - T-SQL : Part 5

Is that enough ? Of course not, you also need Northwind database attached to your database

server (which you can download it from download section of this website) that already widely being

used as sample database from SQL Server 2000. And if you ask, why use Northwind database instead of

Adventure Work database, the main reason is just because its simplicity. Northwind database contains

small number of tables and also it only covers small amount of records, thus beginner will feel

comfortable and fast in doing this lesson.

So, if you already download your Northwind script, then just open your SQL Server Management

Studio and then open the northwind.sql script file. Afterward, execute the script by pressing F5 key, and

that’s it, you will have a newly Northwind database attached to your SQL server.

Prior Knowledge needed

If you really want to follow this series, then you should aware that basic SQL knowledge really

needed. For example, this HOL wil not include any basic knowledge about T-SQL basic command and

also about the basic of SQL server.

And also, you should know the relationship diagram of Northwind database before you

understand this lesson. You can learn about Northwind relationship by creating Database Diagram in

SQL Server Management Studio. Please refer to previous lesson on how to create the diagram.

You also ought to know basic Select command (includes multiple table and aggregation) from

previous lesson (if you are really a beginner), however, if you feel good enough in SQL and merely trying

to improve your skill then just follow the exercises later. Have fun !

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Learning By Sample - T-SQL : Part 5

HAVING

1. In previous lesson, you already try exercises for grouping and aggregating fields. But, what if the

condition in our query is containing aggregate function ? There’s no other way to solve it unless you

use Having keyword. The principal of this keyword is easy, it just the same with common condition,

but it must be started with keyword having and contain aggregate function. Enough for the theory,

let’s roll on…

a. Displaying category name which have sales omzet greater than 200 thousands.

Here is the result :

So, where’s the keyword go ? Focus on condition after group by clause here :

b. Displaying sales omzet percentage from all transaction which are greater than 150.000 and

sort it from the biggest one.

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Learning By Sample - T-SQL : Part 5

Check the result :

Wow, we have double Cast in this query, this happen because we need to put % symbol

which only fit with varchar type :

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Learning By Sample - T-SQL : Part 5

And check also the desc keyword that we use for sorting :

c. Want to try more complex sample ? Here we go, try to display whole product name which

their sales omzet goes below sales average in 1996

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Learning By Sample - T-SQL : Part 5

Here is the result :

Now, pay attention to having keyword condition, it uses sub query for its comparison

operator.

So, the conclusion is that we must be creative in this query game.

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Learning By Sample - T-SQL : Part 5

NULL

1. What is Null ? For sure, you can say that null is just empty value from a field. However, null value is

not equal with common empty value. For instance, if you fill a numeric field using zero, it’s not the

same with null. Confuse ? Okay then, let me show you the example :

a. Display company name and fax field of customer

Check the highlighted result which shows null value

b. Display employee’s bos

Here is the result :

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Learning By Sample - T-SQL : Part 5

2. Now, let see how to create condition using this null value

a. Display customer which has no fax number

Let see the result here :

b. Display the highest level in employee

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Learning By Sample - T-SQL : Part 5

Then, who is the highest level ?

3. In next tutorial I’ll try to give you some lessons about batch query, but now I need to enjoy my black

kretek filter first after seeing Manchester United crunching Blackburn Rovers by seven stylish goals,

see ya…...