Question

我的数据库中的表：

CREATE TABLE items (
  id serial NOT NULL,
  user_id integer NOT NULL,
  status smallint
);

CREATE TABLE phones (
  phone character varying,
  users integer[]
);

我的查询找到状态= 1的电话号码：

SELECT phones.phone, COUNT(*) AS "count" 
FROM phones,items 
WHERE phones.phone = ANY (Array['7924445544', '8985545444'])
AND   items.user_id = ALL (phones.users) AND items.status = 1
GROUP BY phones.phone;

查询：

   phone    | count
------------+------
 7924445588 |     3

需要ZERO计数：

   phone    | count 
------------+-------
 8985545444 |     0
 7924445544 |     3

如何获得？

Answer 1

你不应该在查询中这样做。但是，如果你想要这样做，那就很容易了：

WITH phone_seek AS(
   SELECT '8985545444' AS phone
   UNION ALL
   SELECT '7924445588 '
)
SELECT  phone_seek.phone, COUNT(items.id) AS "count"
FROM 
  phones_seek
  JOIN phones
    ON phones_seek.phone = phones.phones
  CROSS JOIN items
WHERE 
  items.user_id = ALL (phones.users) AND items.status = 1 
GROUP BY phones.phone;

Answer 2

创建不存在的行有点棘手。（其中有数十亿，至少......）如果手机不存在，请使用带有选择的UNION ALL来提供您想要的结果。

<current query>
UNION ALL
select '8985545444',0
from one_row_table where not exists (select 1 from phones
                                     where phones.phone = '8985545444')

修改如果电话号码确实存在但未满足WHERE子句条件，请使用相关子选项进行计数：

SELECT phones.phone, (select count(*) from items where items.status = 1 and items.user_id = phones.users) as "Count" FROM phones WHERE phones.phone = ANY (Array['7924445544', '8985545444'])

Answer 3

Count是一个聚合函数，通常数据库引擎在没有符合条件的行时产生计数。

您的查询没有产生结果的原因是在db和group by中包含了您的phones.phone字段。

1）对此的廉价解决方案是仅选择count（*）作为您的应用程序已经知道电话号码了：

SELECT  COUNT(*) AS "count"
FROM phones, items
WHERE phones.phone = '8985545444'
  AND items.user_id = ALL (phones.users) AND items.status = 1 ;

2）理想的解决方案是处理0结果的应用程序由db。返回。

3）如果您需要db来完成所有工作，您可以使用以下内容：

SELECT  phones.phone, COUNT(*) AS "count"
FROM phones, items
WHERE phones.phone = '8985545444'
  AND items.user_id = ALL (phones.users) AND items.status = 1 
GROUP BY phones.phone;
UNION ALL
select '8985545444',0
from one_row_table where not exists (select 1 from phones
                                     where phones.phone = '8985545444')

Answer 4

我不熟悉PostreSQL的数组语法，但这似乎只是一个简单的外连接：

SELECT phones.phone, COUNT(items.user_id) AS "count" 
FROM phones LEFT JOIN items 
  ON items.user_id = ALL (phones.users) 
 AND items.status = 1
WHERE phones.phone = ANY (Array['7924445544', '8985545444']) 
GROUP BY phones.phone;

SELECT COUNT（*）GROUP BY输出零行

4 个答案: