Select Distinct SQL Server

Hello Dev, welcome to our guide on Select Distinct SQL Server. In this article, we will be exploring all you need to know about the Select Distinct function in SQL Server. This function is powerful and essential for database administrators, analysts, and developers alike. We will be covering everything from the basics to advanced queries, tables, and frequently asked questions. Let’s dive in!

Introduction to Select Distinct in SQL Server

The Select Distinct function is a powerful tool that allows you to query a database and retrieve only unique values from specified columns. This tool is incredibly useful when working with large databases where data duplication can cause data inconsistencies and performance issues. In this section, we will cover the basic syntax and usage of Select Distinct in SQL Server.

The Basic Syntax of Select Distinct

The basic syntax of Select Distinct is as follows:

SELECT DISTINCT column_name(s)	FROM table_name	WHERE condition

As you can see, the syntax is similar to a regular Select statement, but with the addition of the DISTINCT keyword. This keyword specifies that only unique values should be returned.

Using Select Distinct on Multiple Columns

You can also use Select Distinct on multiple columns by specifying each column name separated by a comma:

SELECT DISTINCT column_name1, column_name2	FROM table_name	WHERE condition

This will return only unique combinations of the specified columns.

Using Select Distinct with Aggregate Functions

Select Distinct can also be used with aggregate functions such as COUNT, AVG, and SUM.

SELECT COUNT(DISTINCT column_name)	FROM table_name	WHERE condition

This will return the count of unique values for the specified column.

Advanced Queries using Select Distinct

Now that we have covered the basics of Select Distinct, let’s delve into some more advanced queries that can be achieved using this function.

Select Distinct with Order By

You can use Select Distinct with an Order By clause to sort the unique values in ascending or descending order:

SELECT DISTINCT column_name	FROM table_name	WHERE condition	ORDER BY column_name ASC/DESC

This will return only unique values for the specified column, sorted in either ascending or descending order.

Select Distinct with Joins

Select Distinct can also be used with Joins to query data from multiple tables:

SELECT DISTINCT table1.column_name, table2.column_name	FROM table1	INNER JOIN table2 ON table1.column_name = table2.column_name	WHERE condition

This will return only unique combinations of the specified columns from both tables.

Select Distinct with Count and Group By

Select Distinct can also be used with Count and Group By to group the unique values and count the occurrences:

SELECT column_name, COUNT(DISTINCT column_name)	FROM table_name	WHERE condition	GROUP BY column_name

This will group the unique values for the specified column and return the count of occurrences for each unique value.

FAQs About Select Distinct in SQL Server

Q: Is Select Distinct case sensitive?

A: Yes, Select Distinct is case sensitive. This means that if you have two values in a column that are the same but have different cases (e.g. “John” and “john”), they will be treated as distinct values.

Q: Can I use Select Distinct with text or varchar data types?

A: Yes, Select Distinct can be used with text and varchar data types. However, it may impact performance on larger tables due to the data size and complexity of the queries.

Q: Can I use Select Distinct on multiple columns?

A: Yes, Select Distinct can be used on multiple columns. This will return only unique combinations of the specified columns.

Q: Can I use Select Distinct with Joins?

A: Yes, Select Distinct can be used with Joins to query data from multiple tables. This will return only unique combinations of the specified columns from both tables.

Q: Can I use Select Distinct with aggregate functions?

A: Yes, Select Distinct can be used with aggregate functions such as COUNT, AVG, and SUM. This will count the occurrences of unique values for the specified column(s).