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Removing duplicate rows in MySQL
schedule Aug 10, 2023
Last updated local_offer
Tags 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 n2WHERE 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).
Published by Arthur Yanagisawa
Edited by 0 others
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