如何使用postgresql删除python中三列组合的重复项

我想仅在三列(名称,价格和新价格)与相同数据匹配时删除重复数据.但在另一个python脚本中.

所以数据可以插入数据库,但是使用其他python脚本,我想通过cron作业删除这些重复数据.

所以在这种情况下：

cur.execute("INSERT INTO cars VALUES(8,'Hummer',41400, 49747)")

cur.execute("INSERT INTO cars VALUES(9,'Volkswagen',21600, 36456)")

是重复的.插入数据的示例脚本：

import psycopg2
import sys

con = None

try:
    con = psycopg2.connect(database='testdb', user='janbodnar')    
    cur = con.cursor()

    cur.execute("CREATE TABLE cars(id INT PRIMARY KEY, name VARCHAR(20), price INT, new price INT)")
    cur.execute("INSERT INTO cars VALUES(1,'Audi',52642, 98484)")
    cur.execute("INSERT INTO cars VALUES(2,'Mercedes',57127, 874897)")
    cur.execute("INSERT INTO cars VALUES(3,'Skoda',9000, 439788)")
    cur.execute("INSERT INTO cars VALUES(4,'Volvo',29000, 743878)")
    cur.execute("INSERT INTO cars VALUES(5,'Bentley',350000, 434684)")
    cur.execute("INSERT INTO cars VALUES(6,'Citroen',21000, 43874)")
    cur.execute("INSERT INTO cars VALUES(7,'Hummer',41400, 49747)")
    cur.execute("INSERT INTO cars VALUES(8,'Hummer',41400, 49747)")
    cur.execute("INSERT INTO cars VALUES(9,'Volkswagen',21600, 36456)")
    cur.execute("INSERT INTO cars VALUES(10,'Volkswagen',21600, 36456)")

    con.commit()

except psycopg2.DatabaseError, e:
    if con:
        con.rollback()

    print 'Error %s' % e    
    sys.exit(1

finally:    
    if con:
        con.close()

解决方法:

您可以在一个语句中执行此操作,而无需额外往返服务器.

DELETE FROM cars
USING (
    SELECT id, row_number() OVER (PARTITION BY name, price, new_price
                                  ORDER BY id) AS rn
    FROM   cars
    ) x
WHERE cars.id = x.id
AND   x.rn > 1;

需要Postgresql 8.4或更高版本的window function row_number().
在一组欺骗中,最小的身份存活下来.
请注意,我将“新价格”更改为new_price.

或者使用EXISTS半连接,即@wildplasser发布评论相同的效果.

或者,通过CTE-deVotee @wildplasser的特殊要求,用CTE而不是子查询…