SQL Tips, Tricks, and Training - SQL Training Online

The SQL Distinct clause in the SQL Language allows you to remove any repeated data in a column.

Let’s take a look at the following table/query:

select * from customer;

Here are the results from that query:

We have 6 rows and 4 columns in this table, but I only want to look at the customer_company column.

Here is the query to bring back just that column:

select customer_company from customer;

With the following results:

Now, I want to remove the repeated companies. So if you look at “Dell” in the picture above, you will see that it is in there twice.

That is where the “Distinct” clause comes in. Take a look at what happens when I put distinct into the following query:

select distinct customer_company from customer;

I get the following results:

Notice how we only have 5 rows. That is because the extra/repeated Dell row has been removed.

So that is what the distinct clause does, it removes the repeated data elements in a column.

Please post any questions or comments below.

The basis for retrieving data from a relational database like Microsoft SQL Server, Oracle, and MySQL is the SQL Select Statement.

The minimal SQL Select Statement if you were trying to get data from a table named “Customer” would be:

select * from customer;

Here are the results from that query:

You can see that we have a table. You might say it looks like a Microsoft Excel spreadsheet.

It has columns: customer_number, customer_name, customer_company, salesman_employee_number.

And, it has 6 rows.

So there are two keys to the Select statement above.

First:

select *

The “Select” word is a keyword that you start your query with.

The “*” means we want all columns from the table.

Second:

from customer;

The “from” word is a keyword that says you are getting ready to tell the database what table you want.

The “customer” word means you want that table.

The final thing to notice is the “;”. This tells the database that you are done with your Select Statement.

It is optional in Microsoft SQL Server, but it is good to know about.

Now, if you only wanted to bring back the customer_name and the customer_company from the table,

the query (select statement) would be as follows:

select customer_name,customer_company

from customer;

Here are the results from that query:

And that is the basics of the SQL Select Statement.

Post any questions and comments below. I always read every comment.