如何使这个联合查询更有效率？

Question

我在下面使用 UNION 连接创建了 SQL 查询。

如您所见，我查询了同一个 table 两次，但条件略有不同。如果 TYP 是 A 那么它就是一个 Offer。如果TYP为N，AB为真，则为订单。

一切正常。但我猜有更优雅的方式来做到这一点？我希望你能告诉我那是什么！ :)

谢谢。（顺便说一句，如果有所不同，请使用优势 sql）

SELECT
DATUM as report_month,
REGION as region,
count(DISTINCT NUMMER) as order_number,
'Offer' as Type
from xxxxxxxxxxxx
left join xxxxxxxxx on KDNR = anotherDAB.KDNR
WHERE DATUM = '2021-02-16' AND TYP = 'A' 
group by report_month, region

UNION

SELECT
DATUM as report_month,
REGION as region,
count(DISTINCT NUMMER) as order_number,
'Order' as Type
from xxxxxxxxxxx
left join xxxxxxxxx on KDNR = anotherDAB.KDNR
WHERE DATUM = '2021-02-16' AND TYP = 'N' AND AB = true 
group by report_month, region

Answer 1

我怀疑你只是想要条件聚合：

SELECT DATUM as report_month, REGION as region,
       count(DISTINCT NUMMER) as order_number,
       typ
from xxxxxxxxxxxx left join
     xxxxxxxxx
     on KDNR = KDNR
WHERE DATUM = '2021-02-16' AND
      (TYP = 'A' OR TYP = 'N' AND AB = true)
GROUP BY report_month, region, type;

以上将 TYP 保留为 A 或 N。如果需要字符串，可以使用 case 表达式：

(CASE WHEN typ = 'A' THEN 'Offer' ELSE 'Order' END)

如何使这个联合查询更有效率？

how to make this union query more effecient?

sql

union

advantage-database-server