Thursday, July 7, 2011

Creating a simple T-SQL query

For people starting to learn how to write T-SQL queries the first thing you need to know is how to perform a simple query. A query is a way to get information back from a table in a database.

A table should represent a single entity, for example you may have a person table or a product table. We will focus on the person table for this example. A person may have multiple attributes (first name, last name, birth date, sex). These attributes are defined as columns/fields in a table (similar to a row header in a spreadsheet).

The first part of the query is the select statement. You will use the select statement to define what information you want to see pulled from the table. Each field needs to be separated by a comma. If we are only interested in seeing the first name and last name we would write the following.

select first_name, last_name

The statement above will fail to execute because the query is not complete. We have not defined where we wanted to get this information from. For this example table is named "person". In order to declare where we want to get the data from, we use the "from" statement after the list of columns as follows:

select first_name, last_name
from person

That is pretty much the simplest a query will get.