I thought I would try to start offering up some basic SQL query information in layman terms. It is my hopes this will help others to better retrieve information from their database. Please provide feedback, comments or corrections so that others may benefit.
SQL Basics
By Nick Graham
The SELECT Statement
The SELECT statement forms the foundation of any information gathering you want to accomplish from a database. When you use a SELECT statement, you are “querying” or “asking” the database to show you information based on the parameters you define.
A SELECT statement is composed of several keywords, known as clauses, but for this particular discussion I am going to focus on one..the FROM clause. For this example I will use the vcomputer table from the Altiris Notification Server database. Below is some sample data that is representative of what you would find.
Note: This table does not accurately reflect columns and data from the vcomputer table.
Table: vComputer
Name Domain User OS Name OS Version IP Address
Computer1 Altiris Jim Window XP 5.1 192.168.0.1
Computer2 Altiris Andrew Windows 2000 5.0 192.168.15.4
As with any request for information you have to describe what you want and where to get it. The SELECT portion of a query tells the database “Hey, I want information!”. Here is a very basic SQL query structure:
SELECT <column name> FROM <table name>
Lets use our vComputer table above to try it out.
SELECT Name FROM vComputer
This query is asking the database to give you every record from the Name column in the vComputer table. This query would return the following results:
Name
Computer1
Computer2
This information is good but is not very useful by itself. If we modify the SELECT statement a bit we can gather more information. Lets give it a try.
SELECT Name, User FROM vComputer
This query is exactly like the first but we added a second column name
User. You will want to take note that the column names are separated by a comma. You will need to separate each column with a comma remembering that the last column prior to the FROM clause will NOT require a comma. This query would return the following results from our vComputer table.
Name User
Computer1 Jim
Computer2 Andrew
You can add as many columns requests as you would like to the SELECT statement as long as that column exists in the table you are wanting to retrieve data from. You may be saying… “Nick, I want to retrieve everything from the table. Do I have to enter every column name in a SELECT statement?” The answer is no. You can use the asterick in place of the column name to get all the information from a table. Lets look at the SELECT structure for this with the results.
SELECT * FROM vComputer
Using that statement would give you the following information.
Name Domain User OS Name OS Version IP Address
Computer1 Altiris Jim Window XP 5.1 192.168.0.1
Computer2 Altiris Andrew Windows 2000 5.0 192.168.15.4
AS you can see the SELECT statement with the FROM clause gives you access to all the information that a table within your database contains. This concludes the first part of SQL Basics. I will follow up next time with the WHERE clause which will define a search condition.
*My apologies for the poor formatting of the tables. I'll work on making it more presentable.
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