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Finding duplicate values in MySQL

schedule Mar 5, 2023
Last updated
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MySQL
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This can be done using the COUNT method.

SELECT column, COUNT(column)
FROM table
GROUP BY column
HAVING COUNT(column) > 1;

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.

Basic usage

To check for duplicate values in the age column:

SELECT age, COUNT(age)
FROM drivers_license
GROUP BY age
HAVING COUNT(age) > 1;
+------+------------+
| age | COUNT(age) |
+------+------------+
| 17 | 2 |
+------+------------+

The result shows that we have two records with age 17.

robocat
Published by Arthur Yanagisawa
Edited by 0 others
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