Question

考虑下表。它已从CSV导入，但没有主键。

+-----------+----------+----+----+----+
| firstname | lastname | c1 | c2 | c3 |
+-----------+----------+----+----+----+
| johnny    | bravo    | a  | b  | c  |
| bruce     | willis   | x  | y  | x  |
| john      | doe      | p  | q  | r  |
| johnny    | bravo    | p  | q  | r  |
| johnny    | bravo    | p  | q  | r  |
| bruce     | willis   | x  | y  | z  |
+-----------+----------+----+----+----+

我想删除表中不止一次出现（firstname，lastname）的所有行。所以输出将是：

+-----------+----------+----+----+----+
| firstname | lastname | c1 | c2 | c3 |
+-----------+----------+----+----+----+
| john      | doe      | p  | q  | r  |
+-----------+----------+----+----+----+

Answer 1

在MySQL中，最好的方法是使用join：

delete t
from t join
(
    select t2.firstname, t2.lastname
    from t t2
    group by t2.firstname, t2.lastname
    having count(*) > 1
) t2
    on t.firstname = t2.firstname and
       t.lastname = t2.lastname;

Answer 2

您可以选择以下内容而不是删除。

SELECT * FROM TABLE A
INNER JOIN
(
     SELECT FirstName, LastName, COUNT(firstname) AS num
     FROM TABLE
     GROUP BY FirstName, LastName
) B ON A.FirstName = B.FirstName AND A.LastName = B.LastName
WHERE B.num = 1

但是如果你想删除，那就按照以下方式执行

DELETE A 
FROM TABLE A
INNER JOIN
(
     SELECT FirstName, LastName, COUNT(firstname) AS num
     FROM TABLE
     GROUP BY FirstName, LastName
) B ON A.FirstName = B.FirstName AND A.LastName = B.LastName
WHERE B.num > 1

Answer 3

delete from table_name n 
where (select count(*) from table_name z 
where n.firstname  = z.firstname  and n.lastname  = z.lastname) > 1

删除mysql表中的所有重复项

3 个答案: