# [SOLVED] How to count duplication items?

## Issue

Every customer should not have duplicated code, as you can see the result below for example Customer-A have duplicated Code of `22` and Customer-D have duplicated Code of `44`

I like to run a query to get a number of how many duplications do we have, from the result below it should be 4. I have tried using `Group By` Code and `Having` but not having much luck.

``````customer         Code
------        ---------
A               11
A               22
A               22
B               33
C               22
D               44
D               44
D               44
D               22
``````

## Solution

We can use group by and keep the combinations with more than one line

``````create table t(
customer  char(1),
Code int);
insert into t values
('A',               11),
('A',               22),
('A',               22),
('B',               33),
('C',               22),
('D',               44),
('D',               44),
('D',               44),
('D',               22);
``````
``````SELECT
customer,
code,
count(*) "number"
FROM t
GROUP BY
customer,
code
HAVING
COUNT(*) > 1;
``````
```customer | code | number
:------- | ---: | -----:
A        |   22 |      2
D        |   44 |      3
```

db<>fiddle here