postgresql - How to write select statement with a condition of case-insensitive from a select query output

Question

I'm getting data like this

• Doha
• doha
• Dubai
• Abu Dhabi
• Abu dhabi

from the query select distinct(trim(name)) as loc from locations order by trim(name)

Now I want to remove duplicates using lower() or upper() and select the first record . If I use lower function like below,

select distinct(lower(A.loc)) from( select distinct(trim(name)) as loc from locations order by trim(name) ) as A order by lower(A.loc);

it gives result converted to lower as below.

• doha

• dubai

• abu dhabi

  But I want original result as previously mentioned.

• Doha

• Dubai

• Abu Dhabi

Answer 1

演示：db<>小提琴

SELECT DISTINCT ON (lower(city))
    city
FROM
    cities

DISTINCT ON取任意列并给出第一个重复项。在这种情况下，会在内部创建一个全部小写的列。然后取第一条记录，但只取原始列。

---

注意您没有特殊订单。它将采用随机顺序（例如数据在内部存储的方式）。要实现大写值，您必须编写：

SELECT DISTINCT ON (lower(city))
    city
FROM
    cities
ORDER BY lower(city), city DESC

演示：db<>小提琴

这ORDER BY lower(city)是必要的，因为DISTINCT ON需要给定的列是第一个排序的。之后，您可以按任何其他列订购。ORDER BY column DESC将大写字母移到顶部。