postgresql 编写一个物化视图查询以包括基本记录和没有匹配的记录

Question

我有两个 table，一个是用户，另一个是 postgresql 中的订单。

用户table

userid  | username  | usertype
1       |   John    |  F
2       |   Bob     |  P

订单table

userid  |   orderid | ordername
1       |   001     |   Mobile
1       |   002     |   TV
1       |   003     |   Laptop
2       |   001     |   Book
2       |   002     |   Kindle

现在我想为 postgresql 实体化视图编写一个查询，它会给我如下输出

userid  | username | Base Order Name |No of Orders | User Type
1       | John     | Mobile          |  3          |  F - Free
2       | Bob      | Book            |  2          |  P- Premium

我试过下面的查询，但它给出了 5 条记录而不是 2 条记录，并且没有弄清楚如何显示用户类型 F - Free / P - Premium

CREATE MATERIALIZED VIEW userorders
TABLESPACE pg_default
AS
SELECT
u.userid,
username,
(select count(orderid)  from orders where userid = u.userid)
as no_of_orders,
(select ordername  from orders where orderid=1 and userid = u.userid)
as baseorder
FROM users u
INNER JOIN orders o ON u.userid = o.userid
WITH DATA;

结果如下

userid | username | no_of_orders | baseorder
1      | John     | 3            | Mobile
1      | John     | 3            | Mobile
1      | John     | 3            | Mobile
2      | Bob      | 2            | Book
2      | Bob      | 2            | Book

假设基本订单 ID 始终为 001。在最终的物化视图中，用户类型将 return F - Free/ P - Premium 通过查询中的某些映射。

Answer 1

使用分组依据，这变得非常简单。唯一稍微复杂的部分是获取基本订单名称，但这可以使用 FILTER:

select users.userid,
       username,
       max(ordername) FILTER (WHERE orderid='001') as "Base Order Name",
       count(orderid) as "No of Orders",
       CASE WHEN usertype = 'F' THEN 'F - Free'
            WHEN usertype = 'P' THEN 'P- Premium'
       END as "User Type"
FROM users
JOIN orders on users.userid = orders.userid
GROUP BY users.userid, users.username, users.usertype;

postgresql 编写一个物化视图查询以包括基本记录和没有匹配的记录

postgresql write a materialized view query to include base record and no of records matching

postgresql

rdbms

用户table

订单table