Question

我试图在不存在的值中显示0

|people|
  |client|  |sex|  |city_id|         
    MATT      1      1
    STEVE     1      2

|cities|
   |id|   |name|
     1      EEUU
     2      BRASIL 
     3      ARGENTINA
     4      JAPAN

我试图在city = 3和city = 4时显示一个值，如下所示：

|people|
   |client|  |sex|  |city_id|         
     0          0      0
     0          0      0

以下是查询：

SELECT  * FROM people
WHERE sex =1 AND city_id IN(3,4)

有人可以帮我这个吗？感谢

Answer 1

您需要一张城市表，告诉您要显示数据的城市。然后从该城市表到您的人员表中进行OUTER JOIN。

基于编辑：

select coelesce(p.client, '0') client, coalesce(p.sex,0) sex, coalesce(p.city_id, 0) city_id
from cities c
left join people p on p.city_id = c.id

我们仍然需要更好地了解您希望如何处理您拥有的数据。例如，我怀疑你想要按城市的客户进行分组，并显示总和或计数。

Answer 2

您可以使用以下查询来获取所有城市的结果，其中包含＆＃39; 0＆＃39;对于没有关联人的城市的每一个价值。

SELECT  COALESCE(P.name, '0') AS client
        ,COALESCE(P.sex, '0') AS sex
        ,COALESCE(P.city, '0') AS city_id
FROM cities AS C
LEFT OUTER JOIN people AS P ON P.city = C.id;

从城市表中显示city_id可能更有意义，例如：

SELECT  COALESCE(P.name, '0') AS client
        ,COALESCE(P.sex, '0') AS sex
        ,C.id AS city_id
FROM cities AS C
LEFT OUTER JOIN people AS P ON P.city = C.id;

查看fiddle。

如果值不存在，如何显示0？

2 个答案: