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Using SELECT statements

From: SQL Server 2008 Essential Training

Video: Using SELECT statements

Let's begin by going through some simple SQL to read or retrieve information from our database. I am going to open up SQL Server Management Studio and connect to my instance here. After it's open, the button that I am going to click is this one, the New Query button on the toolbar. A query, well, that's the Q in SQL. It's Structured Query Language. We write queries and this one will use the most common piece of SQL, the SELECT statement. We are selecting or choosing information from one of the tables in one of our databases.

Using SELECT statements

Let's begin by going through some simple SQL to read or retrieve information from our database. I am going to open up SQL Server Management Studio and connect to my instance here. After it's open, the button that I am going to click is this one, the New Query button on the toolbar. A query, well, that's the Q in SQL. It's Structured Query Language. We write queries and this one will use the most common piece of SQL, the SELECT statement. We are selecting or choosing information from one of the tables in one of our databases.

So I am going to write this phrase to begin with SELECT *, using the asterisk, From. I want to get everything from somewhere. Well, there's the question. Which database? Which table? Because in SQL Server Management Studio I can see that I have got quite a few databases, even the system databases. And I could be writing a select statement that goes against any of them. So I am first going to have to say which database I'm coming from. So I'm going to say I want to use AdventureWorksLT. So I will type A and I immediately get this IntelliSense, this auto complete that pops up which is great.

I am going to come down with my cursor key to AdventureWorksLT and that's the one that I am going to use, the LT version, then do a dot, and then instead of getting directly to the tables, I am getting to the schemas and roles here. I will explain that in just a second. But for the moment, I will select SalesLT., come down to Customer. This is actually a complete SQL query. I don't need to finish it with a semicolon or anything like that. I can actually go ahead and run or execute this either by clicking this button that says Execute or I could hit the F5 key on my keyboard.

It would do the same thing. Down here it says Query executed successfully. It took 847 rows of data out of the database and it's now showing them to me. It is just a select, so you're not going to find these are editable. We are just reading this information. By convention, you'll see that the SQL keywords such as Select and Insert and Update and From, and we will see quite a few of them, are written in uppercase. It actually doesn't matter. SQL Server Management Studio and even SQL Server is not going to care.

I could just as easily write select in all lowercase and it would work as well. But by convention of many, many years you tend to see SQL statements written with the keywords in uppercase. If we were going to write a lot of SQL statements, it would get a little tedious. You'd have to write the name of the database again and again and again, because typically you are going against the same database all the time. But I do have to say which database I'm interested in. There's a couple of ways to do it. I can put it in the From part to say explicitly what table and what scheme and what database.

Another way that I could do it if I was going to write many SQL statements is before the first one, I just have the phrase Use AdventureWorksLT. This would do exactly the same thing. If I hit Execute again, I will see the same results. Another way that I could do it, if you notice that this Use AdventureWorksLT, we've also got it popping up here. This is the equivalent. It's actually selecting the database that we are interested in right now. So, I can also get rid of that and just make sure that the correct database is showing up in SQL Server Management Studio.

Execute and there we go. It's a common problem for beginners that you're writing a piece of SQL and you think it's correct, but without you noticing it, the wrong database is highlighted. Say master is the very common default database and when you execute, it says "I have no idea what this SalesLT.Customer is." So I will make sure I'm on the right one. Now I am using the SELECT * here. SELECT * just means select everything.

Give me every column in this particular table. While that's nice and convenient when you're in SQL Server Management Studio, you probably don't want to end up doing that. Because when you're writing say an application, of course the database may change. So you want to be very specific about the columns you are going to retrieve. All I can see that I have things like FirstName, MiddleName, LastName, SalesPerson, his EmailAddress is here. So I can instead of using the asterisks, I can say I would like FirstName. And you notice I have IntelliSense there. Comma, LastName, comma, EmailAddress From SalesLT Customer.

I can break this up onto another line as well. This will work just fine. If I hit Execute now, then I get a filtered amount of data. This is what you want to do as a general rule unless you are writing really casual SQL statements. Be specific about the columns that you're interested in. Now, if we were writing this SQL because, for example, we were going to be printing this information on a report, we might even want to combine the FirstName and LastName. Even though they are stored separately in the database, which is a really good way of filtering and sorting things, combining them there is a way we are going to write them out in a report or an email.

Well, we can combine them on the fly within SQL. I can actually instead of using the comma here, I could use the plus sign to concatenate or join these two together. Now, if I just use the plus sign, we are going to have a problem. If I hit Execute, what I am going to see is we are combining or concatenating these two together into this and it says, "Well, there's no column name." It is no FirstName or LastName. It's kind of something in-between. Not only that, but we have the FirstName and LastName squished up against each other.

Well, we'll fix that in two ways. One is I am going to say that rather than combine FirstName and LastName directly together, I'm going to combine them with a space in the middle. Now, when we are doing a space or a string, we use the single quotes to separate it. So I am doing single quote, space, single quote. Add FirstName, then a space, add LastName. We will execute that and that looks a little better in the values that we are getting back, but it still says No column name. It probably be useful to have a kind of madeup or constructed column name here.

The way we do it is this. We are saying I want to select FirstName and space and LastName AS FullName. There isn't a FullName column in that table. So not a problem there. But we can make it seem like there is. So I execute that and now it seems like we are retrieving the FullName column and the EmailAddress. So what we've seen very quickly is just by using a few little key phrases, we can start to get very flexible about the information that we're retrieving. Now, right now I'm bringing back 847 rows. That might not be what I want.

We are going to go ahead and start adding on to this simple SELECT statement where we are saying select the data that we want from the table that we are interested in. But we need to move on and make sure that we are only retrieving the data in the right circumstance or in the right order or when certain conditions are true. So we are going to build on that next.

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This video is part of

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SQL Server 2008 Essential Training

74 video lessons · 36416 viewers

Simon Allardice
Author

 
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  1. 2m 21s
    1. Welcome
      1m 19s
    2. Using the exercise files
      1m 2s
  2. 17m 58s
    1. SQL Server core concepts
      9m 4s
    2. SQL Server editions
      3m 8s
    3. Applications included with SQL Server
      5m 46s
  3. 26m 1s
    1. Preparing for installation
      3m 44s
    2. Creating service accounts
      2m 33s
    3. Installing SQL Server
      11m 42s
    4. Post-installation checks
      3m 9s
    5. Installing sample databases
      4m 53s
  4. 13m 35s
    1. Introduction to SQL Server Management Studio
      8m 7s
    2. Introduction to SQL Server Books Online
      3m 6s
    3. SQL Server system databases
      2m 22s
  5. 1h 26m
    1. Planning your database
      9m 39s
    2. Creating a SQL Server database
      4m 7s
    3. Creating tables
      7m 51s
    4. Data types in SQL Server
      12m 25s
    5. Defining keys
      8m 9s
    6. Creating default values
      4m 39s
    7. Creating check constraints
      2m 25s
    8. Creating unique constraints
      4m 34s
    9. Introduction to relationships and foreign keys
      9m 51s
    10. Creating relationships in SQL Server Management Studio
      8m 14s
    11. Database normalization
      11m 47s
    12. Creating computed columns
      3m 10s
  6. 23m 11s
    1. Using the SQL Server Import and Export Wizard
      3m 58s
    2. Importing Excel files into SQL Server
      6m 11s
    3. Importing CSV files into SQL Server
      5m 27s
    4. Importing Access databases into SQL Server
      7m 35s
  7. 55m 29s
    1. Introduction to Transact-SQL
      3m 43s
    2. Using SELECT statements
      7m 16s
    3. Changing the default database
      2m 21s
    4. Creating conditions in SQL
      8m 10s
    5. Sorting your output
      3m 23s
    6. Using aggregate functions
      7m 12s
    7. Finding unique values
      2m 14s
    8. Joining multiple tables together
      8m 0s
    9. Using subqueries
      9m 33s
    10. Viewing execution plans
      3m 37s
  8. 19m 36s
    1. Writing INSERT statements
      5m 47s
    2. Writing UPDATE statements
      4m 38s
    3. Writing DELETE statements
      2m 54s
    4. Using the OUTPUT clause to return inserted keys and GUIDs
      6m 17s
  9. 32m 52s
    1. Introduction to SQL functions
      6m 26s
    2. Using SQL configuration functions
      2m 14s
    3. Using string functions
      7m 26s
    4. Using date functions
      6m 27s
    5. Creating user-defined functions
      10m 19s
  10. 28m 46s
    1. Introduction to stored procedures
      4m 23s
    2. Creating stored procedures
      11m 23s
    3. Introducing transactions
      4m 23s
    4. Creating transactions
      8m 37s
  11. 16m 39s
    1. Understanding and creating indexes
      6m 32s
    2. Monitoring and rebuilding indexes
      6m 0s
    3. Monitoring database size and integrity
      4m 7s
  12. 11m 41s
    1. Creating backups
      4m 21s
    2. Creating differential backups and using backup compression
      3m 40s
    3. Restoring databases
      3m 40s
  13. 17m 40s
    1. Introduction to SQL Server security and permissions
      5m 54s
    2. Adding a Windows user to the database
      5m 7s
    3. Creating SQL Server logins and switching authentication modes
      6m 39s
  14. 36m 41s
    1. Introduction to SQL Server Reporting Services
      2m 52s
    2. Connecting to the Report Manager
      4m 29s
    3. Using Report Builder
      12m 4s
    4. Formatting values in reports
      4m 17s
    5. Adding indicators to reports
      5m 11s
    6. Adding charts to reports
      3m 54s
    7. Working with report security
      3m 54s
  15. 24m 41s
    1. Introduction to SQL Server Integration Services (SSIS)
      1m 57s
    2. Using Business Intelligence Development Studio (BIDS)
      6m 59s
    3. Creating and executing a simple SSIS package
      7m 35s
    4. Importing packages into SQL Server Management Studio
      3m 21s
    5. Scheduling jobs with SQL Server Agent
      4m 49s
  16. 31s
    1. Goodbye
      31s

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