如何在HAVING子句中使用CASE语句

Question

我试图在网站上搜索有关此主题的答案，但找不到任何能回答我问题的内容。 我觉得这很简单。

我正在编写一个简单的SQL查询来帮助查找未凭证的采购订单，并且取决于采购订单类型是Purchase还是Credit，它在HAVING子句中需要不同的逻辑。 为了获取数据，我不得不编写两个不同的查询。 请参见下面的代码示例

采购订单

select 
prchseordr_id as 'PO ID',
max(prchseordr_dte_rqstd) as DateRequested,
max(prchseordr_type) as POType,
max(vndr_nme) as Vendor, 
sum(imhstry_qntty_ordrd) as QuantityOrdered,
sum(imhstry_qntty_invcd_ap) as QuantityVouchered
from imhstry
join prchseordr on imhstry.imhstry_ordr_id = prchseordr.prchseordr_id
join brnch on prchseordr.brnch_rn = brnch.brnch_rn
join vndr on prchseordr.vndr_rn = vndr.vndr_rn
where prchseordr_dte_rqstd between '2016-01-01' and '2016-04-01'
and prchseordr_type = 'PURCHASE'
group by prchseordr.prchseordr_id
HAVING sum(imhstry_qntty_invcd_ap) < sum(imhstry_qntty_ordrd)
order by prchseordr_id asc 

信贷订单

select 
prchseordr_id as 'PO ID',
max(prchseordr_dte_rqstd) as DateRequested,
max(prchseordr_type) as POType,
max(vndr_nme) as Vendor, 
sum(imhstry_qntty_ordrd) as QuantityOrdered,
sum(imhstry_qntty_invcd_ap) as QuantityVouchered
from imhstry
join prchseordr on imhstry.imhstry_ordr_id = prchseordr.prchseordr_id
join brnch on prchseordr.brnch_rn = brnch.brnch_rn
join vndr on prchseordr.vndr_rn = vndr.vndr_rn
where prchseordr_dte_rqstd between '2016-01-01' and '2016-04-01'
and prchseordr_type = 'CREDIT'
group by prchseordr.prchseordr_id
HAVING sum(imhstry_qntty_invcd_ap) = '0' 
order by prchseordr_id asc 

我想要将这两个查询合并为一个，但是当我尝试使用HAVING子句中的CASE语句将它们合并时遇到了错误。 最近的尝试是在HAVING子句中的=和<符号上抛出语法错误。 我显然错过了一些重要的事情。

select 
prchseordr_id as 'PO ID',
max(prchseordr_dte_rqstd) as DateRequested,
max(prchseordr_type) as POType,
max(vndr_nme) as Vendor, 
sum(imhstry_qntty_ordrd) as QuantityOrdered,
sum(imhstry_qntty_invcd_ap) as QuantityVouchered
from imhstry
join prchseordr on imhstry.imhstry_ordr_id = prchseordr.prchseordr_id
join brnch on prchseordr.brnch_rn = brnch.brnch_rn
join vndr on prchseordr.vndr_rn = vndr.vndr_rn
where prchseordr_dte_rqstd between '2016-01-01' and '2016-04-01'
group by prchseordr.prchseordr_id
HAVING CASE WHEN prchseordr_type = 'Credit' THEN sum(imhstry_qntty_invcd_ap) = '0' 
OR CASE WHEN prchseordr_type = 'Purchase' THEN sum(imhstry_qntty_invcd_ap) < sum(imhstry_qntty_ordrd)
order by prchseordr_id asc 

任何想法或帮助将不胜感激。

Answer 1

在整个case表达式上使用聚合。

select 
prchseordr_id as "PO ID",
max(prchseordr_dte_rqstd) as DateRequested,
prchseordr_type as POType,
max(vndr_nme) as Vendor, 
sum(imhstry_qntty_ordrd) as QuantityOrdered,
sum(imhstry_qntty_invcd_ap) as QuantityVouchered
from imhstry
join prchseordr on imhstry.imhstry_ordr_id = prchseordr.prchseordr_id
join brnch on prchseordr.brnch_rn = brnch.brnch_rn
join vndr on prchseordr.vndr_rn = vndr.vndr_rn
where prchseordr_dte_rqstd between '2016-01-01' and '2016-04-01'
group by prchseordr.prchseordr_id,prchseordr_type
HAVING SUM(CASE WHEN prchseordr_type = 'Credit' THEN imhstry_qntty_invcd_ap END) = 0 
OR SUM(CASE WHEN prchseordr_type = 'Purchase' THEN imhstry_qntty_invcd_ap-imhstry_qntty_ordrd END) < 0
order by prchseordr_id asc 

Answer 2

HAVING CASE 
WHEN prchseordr_type = 'Credit' AND sum(imhstry_qntty_invcd_ap) = '0' THEN 1
WHEN prchseordr_type = 'Purchase' AND sum(imhstry_qntty_invcd_ap) < sum(imhstry_qntty_ordrd) THEN 1
ELSE 0 END = 1

这样的事情。