如何比较和提取 2 列 PostgreSQL

Question

I want to extract colums that different in fruit colum but have a same value in fruit_id colum. how's the query? please help

fruit	fruit_id
apple	a1
banana	b1
citrus	c1
manggo	a1
orange	c1

I expected the result is:

fruit	fruit_id
apple	a1
manggo	a1
citrus	c1
orange	c1

Answer 1

We can use exists logic here:

SELECT f1.fruit, f1.fruit_id
FROM fruits f1
WHERE EXISTS (
    SELECT 1
    FROM fruits f2
    WHERE f2.fruit_id = f1.fruit_id AND
          f2.fruit <> f1.fruit
);