[英]Use CTE instead of Subquery in SQL Server
我有以下查詢,它的工作原理足夠好,但有人告訴我,使用CTE
比使用大型子查詢更好。 我對這個概念CONVERT
,並嘗試通過從CASE
語句到SELECT
列表中的最后一個CONVERT
所有內容CASE
起作用,但是我沒有運氣。 有什么技巧可以幫助嘗試使用CTE
而不是子查詢的人嗎? 我需要使用子查詢的原因是我需要將CASE
語句中的日期與其他別名日期之一進行比較,並且不能在WHERE
謝謝。
SQL:
USE PDX_SAP_USER
GO
SELECT *
FROM (
SELECT E.team_member_name [EMPLOYEE], K.business_segment_desc [BUSINESS SEGMENT], G.order_status [GPS ORDER STATUS], H.po_type [PO TYPE], G.order_no [GPS ORDER NO], I.po_number [SAP PO NUMBER], I.shipping_instruct [SAP SHIP MODE], G.shipping_type [GPS SHIP MODE], CASE
WHEN I.shipping_instruct LIKE 'A%'
THEN CONVERT(VARCHAR(12), (I.revised_ex_factory + 10), 101)
WHEN I.shipping_instruct LIKE 'C%'
THEN CONVERT(VARCHAR(12), (I.revised_ex_factory + 5), 101)
END [DESIRED TRANSIT DATE], CONVERT(VARCHAR(12), I.revised_ex_factory, 101) [LAST CONFIRMED DATE ], CONVERT(VARCHAR(12), S.po_estimated_deliv_date, 101) [CURRENT DELIV DATE],
-- 'days_diff'
I.material [MATERIAL], M.description [DESCRIPTION], I.stock_category [STOCK CATEGORY], I.po_ordered_quantity [PO ORDERED QUANTITY], I.po_recvd_quantity [PO RECVD QUANTITY], I.po_balance_quantity [PO BALANCE QUANTITY], I.po_intransit_quantity [PO INTRANSIT QUANTITY], I.plant_code [PLANT], I.direct_ship_code [DS CODE], I.comment [COMMENT]
FROM (
SELECT order_no, order_status, shipping_type
FROM asagdwpdx_prod.dbo.SimoxOrder1
UNION ALL
SELECT order_no, order_status, shipping_type
FROM asagdwpdx_prod.dbo.SimoxOrder2
UNION ALL
SELECT order_no, order_status, shipping_type
FROM asagdwpdx_prod.dbo.SimoxOrder3
) G
INNER JOIN pdx_sap_user..vw_po_header H ON G.order_no = H.ahag_number
INNER JOIN pdx_sap_user..vw_po_item I ON H.po_number = I.po_number
INNER JOIN pdx_sap_user..vw_po_size S ON I.po_number = S.po_number
AND I.po_item_number = S.po_item_number
INNER JOIN pdx_sap_user..vw_mm_material M ON I.material = M.material
INNER JOIN pdx_sap_user..vw_kd_business_segment K ON M.business_segment_code = K.business_segment_code
INNER JOIN adi_user_maintained..scm_po_employee_name E ON I.po_number = E.po_number
WHERE I.po_balance_quantity > 0
AND I.del_indicator NOT IN ('L', 'S')
AND H.PO_TYPE NOT IN ('01', 'UB')
AND I.shipping_instruct IN ('A1', 'A2', 'A5', 'C1', 'C2', 'C3')
AND G.order_status = '40'
) q1
WHERE q1.[DESIRED TRANSIT DATE] <> q1.[CURRENT DELIV DATE]
ORDER BY q1.[SAP PO NUMBER]
派生表和CTE之間的唯一區別(當然不是語法)是CTE允許您編寫自引用的遞歸查詢(也稱為遞歸CTE)。 有時提前將內容抽象到CTE中會更干凈,但這只是優先事項,而不是性能問題。 就我個人而言,我傾向於使用CTE來抽象大的丑陋查詢,但是對於一個相對於另一個而言,並沒有什么強有力的論據。
舉一個簡單的例子,這兩個語句在功能上是相同的
--- using a CTE
;with numbers as
(
select top 10 num = row_number() over (order by (select null))
from sys.all_objects
)
select *
from numbers
-- Using a derived table
select *
from
(
select top 10 num = row_number() over (order by (select null))
from sys.all_objects
) a
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.