Postgres 15

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create table my_table  (my_name varchar(100));

CREATE TABLE

insert into my_table values ('Test1');
insert into my_table values ('Test1');
insert into my_table values ('Test2');
insert into my_table values ('Test3');
insert into my_table values ('Test4');
insert into my_table values ('Test4');
insert into my_table values ('Test4');
insert into my_table values ('Test5');
insert into my_table values ('Test5');
insert into my_table values ('Test10');

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

INSERT 0 1

select * from my_table;

my_name

Test1

Test1

Test2

Test3

Test4

Test4

Test4

Test5

Test5

Test10

SELECT 10

SELECT
    my_name
FROM
    my_table
GROUP BY
    my_name
HAVING 
    COUNT(*) > 1

my_name

Test1

Test4

Test5

SELECT 3

DELETE
FROM my_table 
WHERE my_name IN 
(SELECT
    my_name
FROM
    my_table
GROUP BY
    my_name
HAVING 
    COUNT(*) > 1)

DELETE 7

select * from my_table;

my_name

Test2

Test3

Test10

SELECT 3