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Asked: 2024-09-27T00:19:29+05:30 In:

how do you use distinct in sql

Hi there! I’m currently working with SQL and I’ve run into a bit of a roadblock. I’ve been trying to retrieve unique records from my database, but I’m not entirely sure how to use the DISTINCT keyword correctly.

For example, I have a table called `Customers` with several columns, including `Name`, `City`, and `Country`. If I want to find all the different cities that my customers are from, I think I need to write a query that only gives me distinct city names. However, I keep wondering if I should include other columns in my SELECT statement when using DISTINCT.

Also, I’m confused about how DISTINCT works when multiple columns are involved. If I use DISTINCT with two columns, does it return unique combinations of those two columns, or just one of them? And what about performance—does using DISTINCT slow down my queries significantly, especially with large datasets? Any examples to illustrate how to use DISTINCT effectively would be really helpful! Thanks in advance for your guidance!

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    2 Answers

    1. Using DISTINCT in SQL

      So, like, if you’re trying to get rid of duplicates in your SQL queries, you can use something called DISTINCT. It’s pretty simple actually!

      What does DISTINCT do?

      Basically, when you ask for stuff from a table, sometimes you get repeated things. DISTINCT helps you only get the unique ones. Think of it like a filter to remove those pesky duplicates!

      How to use it?

      Here’s a quick example:

      SELECT DISTINCT column_name FROM table_name;

      This code says, “Hey, give me all the unique values from column_name in table_name!”

      Example Time!

      Let’s say you have a table called users and you wanna get all the unique names:

      SELECT DISTINCT name FROM users;

      This will give you a list of names without any repeats. Yay!

      Some things to keep in mind

      • Only use it if you really need it, ‘cause it can make your query slower with big tables.
      • It can be used with multiple columns too! Like this:
        • SELECT DISTINCT column1, column2 FROM table_name;

      So, that’s about it! Just remember, DISTINCT is your friend when you want to clean up your results!

    2. When using the DISTINCT keyword in SQL, it is essential to understand its role in eliminating duplicate rows from the result set of a query. You typically apply DISTINCT directly after the SELECT keyword to specify that you want unique values returned for given columns. For instance, if you have a table named ‘Employees’ and want to retrieve a list of unique job titles, you would execute a query like SELECT DISTINCT job_title FROM Employees;. This will return a result set that comprises only unique job titles, removing any duplicates inherent in the data.

      Moreover, DISTINCT can also be combined with other clauses to refine your query results further. For example, if you want to find distinct combinations of job titles and departments, you could use: SELECT DISTINCT job_title, department FROM Employees WHERE status = 'active';. It is worth noting that the DISTINCT keyword affects all columns listed in the SELECT statement, meaning that if you specify multiple fields, SQL will return unique combinations of values across those fields. Given that processing DISTINCT can lead to additional overhead, it’s wise to use it judiciously, particularly when dealing with large datasets, as it can impact query performance.

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