SQL在所有列中选择唯一的表行

Question

我有一张表格，其结果如下所示

total_passengers origin_city_name  dest_city_name   year
----------------------------------------------------------------
2926589          New York          Chicago          2009
2926589          Chicago           New York         2009
2876933          Los Angeles       San Francisco    2009
2876933          San Francisco     Los Angeles      2009

如何删除冗余行 - 2＆amp; 4。

由于

Answer 1

如果您不关心在没有第二行时是否可以交换原点和来源：

SELECT DISTINCT
  total_passengers,
  CASE WHEN origin_city_name > dest_city_name 
       THEN dest_city_name 
       ELSE origin_city_name
  END,
  CASE WHEN origin_city_name < dest_city_name 
       THEN dest_city_name
       ELSE origin_city_name
  END,
  year
FROM tab
;

Answer 2

为查询添加WHERE子句，因此您不会获得反向的原始目标记录：

WHERE origin_city_name < dest_city_name

Answer 3

dnoeth's answer略有不同：

SELECT DISTINCT
total_passengers, 
LEAST(origin_city_name, dest_city_name) AS origin_city_name,
GREATEST(origin_city_name, dest_city_name) AS dest_city_name,
year
FROM yourtable;

和here's the fiddle。