Question

我有下表

drop table names;
create table names(
    name    varchar(200),
    surname varchar(200),
    primary key(name, surname)
);

insert into names values ('john', 'doe');
insert into names values ('john', 'richards');

我想列出姓名相同的姓氏。即我想要这个结果

----------+----------
 doe      | richards
 doe      | doe
 richards | richards

（这只是一个例子，真正的问题是完全不同的）

followig查询返回重复项

select n1.surname, n2.surname
from names n1 join names n2
on n1.name = n2.name;

 surname  | surname  
----------+----------
 doe      | richards
 doe      | doe
 richards | richards
 richards | doe

所以，我使用了least和greatest postgresql函数，得到了我的结果。但是：least和greatest不是标准SQL，我想知道是否存在更有效的解决方案，因为使用我现在无法想象的连接条件。

select distinct least(n1.surname, n2.surname), greatest(n1.surname,
n2.surname)
from names n1 join names n2
on n1.name = n2.name;

  least   | greatest 
----------+----------
 doe      | richards
 doe      | doe
 richards | richards

Answer 1

如果您只想要打破平局，请使用＆lt; ＆gt;或＆gt; =或＆lt; =

SELECT n1.surname, n2.surname
FROM names n1 
JOIN names n2 ON n1.name = n2.name
WHERE n1.surname >= n2.surname
   ;

从此SQL连接中删除重复项

1 个答案: