Question

我有以下查询，它运行良好但我被告知使用CTE是一个比巨型子查询更好的路线。我对这个概念很陌生，并尝试通过从CASE语句中的CONVERT语句到SELECT列表中的最后CTE来提取所有内容，但我没有运气。对于试图使用CASE而不是子查询的人，是否有任何提示？我需要使用子查询的原因是我需要将WHERE语句中的日期与其他别名日期进行比较，而不能在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]

中进行比较

感谢。

SQL：

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Answer 1

派生表和CTE（当然不是语法）之间的唯一区别是CTE允许您编写自引用的递归查询（也称为递归CTE）。提前将事物抽象到CTE中有时更清晰，但这只是一个偏好问题，而不是一个表现问题。就个人而言，我倾向于成为使用CTE来抽象丑陋查询的粉丝，但对于其他人而言，这并不是一个强有力的论据。

通过一个简单的例子，这两个陈述在功能上是相同的

 --- 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

在SQL Server中使用CTE而不是子查询

1 个答案: