When it comes to working with databases, there are certain commands and functions that are essential to know in order to retrieve the desired data. Two such commands that are commonly used are SELECT UNIQUE and SELECT DISTINCT. While both of these commands are used to retrieve unique values from a database, there are some key differences between them. In this article, we will explore and compare the SELECT UNIQUE and SELECT DISTINCT commands.
First, let's start with a basic understanding of what these commands do. Both SELECT UNIQUE and SELECT DISTINCT are used to retrieve unique values from a database table. This means that when using these commands, duplicate values will be eliminated from the result set. However, the way in which they achieve this may vary.
SELECT UNIQUE is used to retrieve unique values from a single column in a table. This means that if we have a table with multiple columns, using SELECT UNIQUE will only retrieve unique values from the specified column. On the other hand, SELECT DISTINCT is used to retrieve unique values from multiple columns. This means that if we have a table with multiple columns, using SELECT DISTINCT will eliminate duplicate rows based on all the selected columns.
Another difference between these commands is the way they handle null values. When using SELECT UNIQUE, null values are considered as unique and will be displayed in the result set. On the other hand, SELECT DISTINCT will eliminate null values from the result set.
In terms of performance, SELECT UNIQUE is known to be faster than SELECT DISTINCT. This is because SELECT DISTINCT has to compare values across multiple columns, which can be more time-consuming. However, the difference in performance may not be significant in smaller databases, and it ultimately depends on the size and complexity of your data.
Now let's take a closer look at the syntax of these commands. The syntax for SELECT UNIQUE is as follows:
SELECT UNIQUE column_name FROM table_name;
This will retrieve unique values from the specified column in the table. On the other hand, the syntax for SELECT DISTINCT is as follows:
SELECT DISTINCT column_name1, column_name2 FROM table_name;
This will retrieve unique values from the specified columns in the table. As mentioned earlier, SELECT DISTINCT will eliminate duplicate rows based on all the selected columns.
In summary, the main difference between SELECT UNIQUE and SELECT DISTINCT is the number of columns that they consider when retrieving unique values. SELECT UNIQUE retrieves unique values from a single column, while SELECT DISTINCT retrieves unique values from multiple columns. Additionally, SELECT DISTINCT eliminates null values from the result set, while SELECT UNIQUE includes them.
In conclusion, both SELECT UNIQUE and SELECT DISTINCT are useful commands to retrieve unique values from a database. However, it is important to understand their differences and choose the appropriate command based on your specific needs. With this knowledge, you can efficiently retrieve and work with unique data in your database.
