左连接以从同一视图中分离查询

Question

我对学习 PSQL 还是个新手，想知道如何 LEFT JOIN 我从同一个物化视图中检索的两个单独的查询。

这是我的第一个查询：

select rep_name, Count(enroll_date) new_orders, Sum(invoice_total) contract_total, Avg(invoice_total) avg_contract_total
from recent_billing_mat_view
where
    enroll_date <= current_date
    AND enroll_date > (current_date - '30 days'::interval)
    AND product_type = 'CTF'
    AND pay_type <> 'Credit'
group by rep_name

它 returns 以下内容：

rep_name   new_orders  contract_total avg_contract_total
"Alyssa"    9               2515       279.444444444444
"Carlos"    24              6585       274.375
"Cheryle"   14              4871       347.928571428571
"Nicholas"  19              4775       251.315789473684
"Piero"     13              4405.5     338.884615384615
"Susan"     15              4450.5     296.7
"Valerie"   16              4640       290
"Yelitza"   12              3607       300.583333333333

这是我的第二个查询：

select rep_name,  Count(enroll_date) orders_paid
from recent_billing_mat_view
where
    enroll_date <= current_date
    AND enroll_date > (current_date - '30 days'::interval)
    AND product_type = 'CTF'
    AND pay_type <> 'Credit'
    AND amount_paid > 0
group by rep_name

它 returns 以下内容：

rep_name    orders_paid
"Alyssa"        6
"Carlos"        16
"Cheryle"       8
"Nicholas"      14
"Piero"         9
"Susan"         8
"Valerie"       10
"Yelitza"       9

我正在使用第二个查询来计算已为每个代表支付的所有订单的数量，我想在第一个查询中加入该订单。我目前收到错误：错误：“LEFT”处或附近的语法错误。

这是我正在使用的内容：

select r.rep_name, Count(enroll_date) new_orders, Sum(invoice_total) contract_total, Avg(invoice_total) avg_contract_total
from recent_billing_mat_view r
where
    r.enroll_date <= current_date
    AND r.enroll_date > (current_date - '30 days'::interval)
    AND r.product_type = 'CTF'
    AND r.pay_type <> 'Credit'
group by r.rep_name
LEFT JOIN (
select Count(enroll_date) orders_paid
from recent_billing_mat_view p
where
    p.enroll_date <= current_date
    AND p.enroll_date > (current_date - '30 days'::interval)
    AND p.product_type = 'CTF'
    AND p.pay_type <> 'Credit'
    AND p.amount_paid > 0
group by rep_name
) as p On r.rep_name = p.rep_name

我希望结果看起来像什么：

rep_name   new_orders  contract_total avg_contract_total  orders_paid
"Alyssa"    9               2515       279.444444444444        6
"Carlos"    24              6585       274.375                 16
"Cheryle"   14              4871       347.928571428571        8
"Nicholas"  19              4775       251.315789473684        14
"Piero"     13              4405.5     338.884615384615        9
"Susan"     15              4450.5     296.7                   8
"Valerie"   16              4640       290                     10
"Yelitza"   12              3607       300.583333333333        9

我在这里错过了什么？如果没有 LEFT JOIN，有没有更好的方法来做到这一点？

谢谢！

Answer 1

除了 where 子句中的一个条件外，第二个查询与第一个查询完全相同。您可以只使用条件聚合：

select rep_name, 
    count(*) new_orders, 
    sum(invoice_total) contract_total, 
    avg(invoice_total) avg_contract_total,
    count(*) filter(where amount_paid > 0) orders_paid
from recent_billing_mat_view
where
    enroll_date <= current_date
    and enroll_date > current_date - '30 days'::interval
    and product_type = 'CTF'
    and pay_type <> 'Credit'
group by rep_name

注意：您的查询构建方式，enroll_date 永远不可能是 null（因为它在 where 子句中被过滤）：所以 count(enroll_date) 是等效的count(*)，效率也更高。

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