將 CTE Query 轉換為普通 Query

Question

我想將我的@PostgreSQL CTE 查詢轉換為普通查詢，因為 cte function 主要用於數據倉庫 SQL 並且對於 Postgres 生產 DBS 效率不高。 因此，需要幫助將此 CTE 查詢轉換為普通查詢

WITH
cohort AS (
    SELECT
        *
    FROM (
        select 
        activity_id,
        ts,
        customer,
        activity,
        case 
        when activity = 'completed_order' and lag(activity) over (partition by customer order by ts) != 'email' 
        then null
        when activity = 'email' and lag(activity) over (partition by customer order by ts) !='email' 
        then 1
        else 0
    end as cndn
        
        from activity_stream where customer in (select customer from activity_stream where activity='email') 
        order by ts
) AS s 

)
(
    select 
        *               
      from cohort as s
where cndn = 1 OR cndn is null order by ts)

Answer 1

您可以將 CTE 內聯到外部查詢中：

select *               
from
(
    select activity_id, ts, customer, activity,
           case when activity = 'completed_order' and lag(activity) over (partition by customer order by ts) != 'email' 
                then null
                when activity = 'email' and lag(activity) over (partition by customer order by ts) !='email' 
                then 1
                else 0
           end as cndn
    from activity_stream
    where customer in (select customer from activity_stream where activity = 'email') 
) as s
where cndn = 1 OR cndn is null
order by ts;

請注意，您在 CTE 中有一個不必要的子查詢，它執行ORDER BY無論如何都不會“堅持”。 但除此之外，您可能希望保持當前代碼不變。