Learn SQL in 1 Day: Definitive Guide to Learn SQL for Beginners by Krishna Rungta

Author:Krishna Rungta [Rungta, Krishna]
Language: eng
Format: azw3
Published: 2017-03-19T04:00:00+00:00

The above result has many duplicates.

Let's execute the same query using group by -

SELECT `category_id`,`year_released` FROM `movies` GROUP BY `category_id`,`year_released`;

Executing the above script in MySQL workbench against the myflixdb gives us the following results shown below.

category_id year_released

NULL 2008

NULL 2010

NULL 2012

1 2011

2 2008

6 2007

7 1920

8 1920

8 2005

8 2007

The GROUP BY clause operates on both the category id and year released to identify unique rows in our above example.

If the category id is the same but the year released is different, then a row is treated as a unique one .If the category id and the year released is the same for more than one row, then it's considered a duplicate and only one row is shown.

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