PG数据去重

构造测试数据

CREATE TABLE basket(
    id SERIAL PRIMARY KEY,
    fruit VARCHAR(50) NOT NULL
);	
INSERT INTO basket(fruit) values('apple');
INSERT INTO basket(fruit) values('apple');
INSERT INTO basket(fruit) values('orange');
INSERT INTO basket(fruit) values('orange');
INSERT INTO basket(fruit) values('orange');
INSERT INTO basket(fruit) values('banana');

去重

• 方法1:使用 DELETE USING 语句删除重复的行

DELETE
FROM
    basket a
        USING basket b
WHERE
    a.id < b.id
    AND a.fruit = b.fruit;

• 方法2:使用子查询删除重复的行

DELETE FROM basket
WHERE id IN
    (SELECT id
    FROM 
        (SELECT id,
         ROW_NUMBER() OVER( PARTITION BY fruit
        ORDER BY  id ) AS row_num
        FROM basket ) t
        WHERE t.row_num > 1 );

• 方法3: 使用ctid删除

 delete from basket where ctid not in (select min(ctid) from basket group by id);

• 方法4: 使用ctid删除2

delete  from basket a where a.ctid<>(select min(ctid) from basket b where a.fruit=b.fruit);

视图去重

如果是对于视图进行去重，由于视图没有ctid，所以无法通过ctid去重；
可以使用方法1与2；