仅显示 1 个数据

Question

我尝试查询数据，但是数据多于1，我只想显示1个数据，也就是第一个数据。

查询：

SELECT DISTINCT a.country_id,
                a.street_address,
                a.city,
                a.phone_number,
                a.location_id,
                b.ket
  FROM LOCATIONS a
  LEFT OUTER JOIN (SELECT DISTINCT y.country_id,
                                   y.country_name || ' ' || z.REGION_NAME AS ket
                     FROM countries y, regions z
                    WHERE y.REGION_ID = z.REGION_ID) b
    ON a.country_id = b.country_id;

Answer 1

您可以使用DENSE_RANK() 之类的分析函数，包括按country_id 排序（假设图像中的排序列）以带来第一行（包括平局），例如

SELECT country_id, street_address, city, phone_number, location_id, ket
  FROM
  (
    SELECT l.country_id,
           l.street_address,
           l.city,
           l.phone_number,
           l.location_id,
           c.country_name || ' ' || r.region_name AS ket,
           DENSE_RANK() OVER (ORDER BY l.country_id) AS dr
      FROM locations l
      LEFT JOIN countries c
        ON l.country_id = c.country_id
      LEFT JOIN regions r
        ON c.region_id = r.region_id
    )
  WHERE dr = 1     

Answer 2

如果您只想从查询中获取第一行，请试试这个。

 SELECT DISTINCT a.country_id, a.street_address, a.city, a.phone_number, a.location_id, b.ket FROM LOCATIONS a LEFT OUTER JOIN (SELECT DISTINCT y.country_id, y.country_name || ' ' || z.REGION_NAME AS ket FROM countries y, regions z WHERE y.REGION_ID=z.REGION_ID) b ON a.country_id = b.country_id
order by a.country_id
    fetch first 1 rows only;

（我添加了 order by 子句（假设您想要第一个国家/地区的行）。没有 order by 子句，不能保证每次都有相同的行。）