The DISTINCT Concept in SQL
In SQL, the SELECT operation is used to retrieve data from one or more tables. You might want to obtain non-duplicate data from a table. The SELECT DISTINCT statement is precisely used for this purpose. By using this statement, you can remove duplicate values and only retrieve unique values.
For example, suppose you have a table that contains all the orders of customers. If you want a list of unique customers (without duplicates), you can use the SELECT DISTINCT statement. This statement ensures that each customer appears only once in the result set.
This feature is especially useful in data analysis, as it allows you to focus on unique attributes. However, be aware that the DISTINCT statement may require more processing to eliminate duplicate occurrences, which can impact performance significantly.
How to Use SELECT DISTINCT?
The simplest way to use this statement is as follows:
SELECT DISTINCT column1, column2
FROM table_name;
Now let’s see how this statement works:
First Line:
The SELECT DISTINCT statement specifies that we want to retrieve only unique values from the selected columns.
column1, column2:
In this part, you specify the columns from which you want to retrieve unique values.
Second Line:
The FROM table_name clause specifies which table the data is to be retrieved from.