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SQL 101 – SELECT

The first thing you need to know when learning SQL is how to get data out of a database.  This means learning the SELECT command.  Using this command will get the SQL server to return data to you. You can use this command to do some simple math, or to do the common "Hello World!" application you all learn the first day of a programming course.

SELECT 1 + 1
> 2

SELECT 'Hello World'
>Hello World

Keeping this in mind can become useful later, when you need to have the server return debugging statements to you during particularly long code writing sessions.  But usually you'll need the SELECT command to look up a certain piece of data from a table.  Let's assume you have a table of products.  In this table there are several columns, one of which is productName.  If you wanted to get a list of every product in your table, you can write the following command:

SELECT
   productName
FROM products

output

  productName
  -----------
  pencil
  pen
  paper
  Mountain Dew

I'd like to point out the data returned is not ordered.  In later articles I'll show you how to put the results into any order you may find useful.  But for now, Let's stick to learning about the SELECT statement.

What if you wanted to know the name and the price?  In SQL you can list as many columns as you like, in a comma separated list.

SELECT
   productName, price
FROM products

output

  productName     price
  -----------     -----
  pencil          .25
  pen             .99
  paper          1.00
  Mountain Dew   1.25

Finally, if you want to return all the data of the table, you can do that too.  But I would like to point out using the following command on a table with lots of rows (thousands, or millions) could be very time and processor consuming.  Use this only if you know the number of records and columns will be small enough your server and connection can handle.  There are also many reasons NOT to use this, but I'll show you how to do it anyway.

SELECT
   *
FROM products

output

  productName     price   quantity   color
  -----------     -----   --------   -----
  pencil          .25      100        yellow
  pen             .99       73        blue
  paper          1.00      500        white
  Mountain Dew   1.25        8        green

As always, if you have any questions, please let me know!  I'm here to help you understand SQL better.  Let me know how I can do that.

Related posts:

1. SQL 101 – SELECT, Filtering Results
2. SQL 101 – SELECT, Filtering Results (Part 2)
3. SQL 101 – Combining Query Results
4. SELECT INTO
5. SELECT * Overhead

About Shannon Lowder

Shannon Lowder is the Database Engineer you've been looking for! Look no further for expertise in: Business Analysis to gather the business requirements for the database; Database Architecting to design the logical design of the database; Database Development to actually build the objects needed by the business logic; finally, Database Administration to keep the database running in top form, and making sure there is a disaster recovery plan.