Question

我正在创建一个视图，其中我几乎复制了原始用户的数据，但我还有一个属性，我想在其中列出用户在下载表中出现的次数。

CREATE VIEW customer_count_streams_vw(
sid_customer
systemuser_id
postcode
age
gender
num_streams) 
AS 
SELECT
user.sid_customer,
user.systemuser_id,
user.postcode,
user.age,
user.gender,
num_streams 
FROM md_customer 
INNER JOIN ods_streaming AS num_streams (
SELECT COUNT(ods_streaming.sid_customer) 
WHERE ods_streaming.sid_customer = md_customer.sid_customer)

我想要的是放置部分的结果：

SELECT COUNT(ods_streaming.sid_customer) 
WHERE ods_streaming.sid_customer = md_customer.sid_customer

进入num_streams字段。

Answer 1

您的查询应该是

SELECT
user.sid_customer,
user.systemuser_id,
user.postcode,
user.age,
user.gender,
num_streams 
FROM md_customer 
INNER JOIN 
( 
        SELECT sid_customer, COUNT(ods_streaming.sid_customer) num_streams 
        FROM ods_streaming group by sid_customer
) AS ods_streaming  
ON ods_streaming.sid_customer = md_customer.sid_customer

上面的查询将为md_customer中的行以及ods_streaming中的行返回行。如果您想要所有客户及其计数（包括0），那么您的查询应该是

SELECT
cust.sid_customer,
cust.systemuser_id,
cust.postcode,
cust.age,
cust.gender,
COUNT(strm.sid_customer) num_streams 
FROM 
   md_customer cust
LEFT OUTER JOIN ods_streaming  strm   
   ON cust.sid_customer = strm.sid_customer
group by 
cust.sid_customer,
cust.systemuser_id,
cust.postcode,
cust.age,
cust.gender

Answer 2

也许您可以尝试将group by用于计数，而不是使用子选择。

SELECT
md_customer.sid_customer,
md_customer.systemuser_id,
md_customer.postcode,
md_customer.age,
md_customer.gender,
count(ods_streaming.num_streams)
FROM md_customer 
INNER JOIN ods_streaming 
on ods_streaming.sid_customer = md_customer.sid_customer
group by 1,2,3,4,5;

你应该避免做这样的子选择......这个小组应该让事情更快一点

Answer 3

SELECT
    u.sid_customer,
    u.systemuser_id,
    u.postcode,
    u.age,
    u.gender,
    num_streams.amount
FROM 
    md_customer u INNER JOIN (
            SELECT 
                ods_streaming.sid_customer,
                COUNT(ods_streaming.sid_customer) as amount 
            FROM
                ods_streaming 
            GROUP BY ods_streaming.sid_customer

        ) num_streams  ON ( num_streams.sid_customer = u.sid_customer )

此外：用户是大多数（如果不是全部）数据库引擎的保留字

根据where子句的结果创建别名

3 个答案: