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Removing duplicate rows in MySQL

schedule Aug 10, 2023
Last updated
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MySQL
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We can remove duplicate rows from a table in MySQL using the below general syntax:

DELETE n1 FROM table_name n1, table_name n2
WHERE n1.id_column > n2.id_column AND n1.column_name = n2.column_name

Example

Consider the following table about whether students hold a drivers license:

student_id

full_name

age

has_license

1

Sky Towner

17

0

2

Ben Davis

19

1

3

Travis Apple

18

0

4

Arthur David

16

0

5

Benjamin Town

17

1

The above sample table can be created using the code here.

To remove all rows with duplicate has_license value and keep the record with lowest student_id:

DELETE n1 FROM drivers_license n1, drivers_license n2
WHERE n1.student_id > n2.student_id AND n1.has_license = n2.has_license;

SELECT * FROM drivers_license;
+------------+------------+------+-------------+
| student_id | full_name | age | has_license |
+------------+------------+------+-------------+
| 1 | Sky Towner | 17 | 0 |
| 2 | Ben Davis | 19 | 1 |
+------------+------------+------+-------------+

Within the drivers_license table we search for records which have the same value of has_license (n1.has_license = n2.has_license) from where we proceed to delete the record with the higher student_id (n1.student_id > n2.student_id).

robocat
Published by Arthur Yanagisawa
Edited by 0 others
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