SQL Server Distinct，选择所有行

Question

我已经看到了很多关于这个主题的问题和答案，但我很难理解我到底做错了什么。下面的查询获取了我需要的所有信息，但如果它有多行，当r_num 是相同的，并且每个 r_num 的 r_order 是相同的，那么每个 r_num 我只有一个结果。现在虽然这个调用给了我错误。有人可以向我解释Distinct是如何工作的，以及我如何使用它在这个查询中实现我的目标？

SELECT DISTINCT po_num, r_num, r_order, vendor, order_date, received_by, received_date FROM(
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date
    FROM Parts.dbo.po as p INNER JOIN
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar)
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date) as tbl
GROUP BY r_num, r_order

这是我得到的错误

Msg 8120, Level 16, State 1, Line 1 Column 'tbl.po_num' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Answer 1

除非您进行聚合，否则您不需要同时拥有 DISTINCT 和 GROUP BY。

SELECT DISTINCT po_num, r_num, r_order, vendor, order_date, received_by, received_date 
FROM
  (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date
    FROM Parts.dbo.po as p INNER JOIN
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar)
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date
  ) as tbl

如果您想获得不同的 r_num 和 r_order 值，则需要分组/仅选择这两列：

SELECT r_num, r_order
FROM
  (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date
    FROM Parts.dbo.po as p INNER JOIN
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar)
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date
  ) as tbl
GROUP BY r_num, r_order

或者，如果您的数据可以处理，请在额外列上使用聚合：

SELECT MAX(po_num) AS po_num, r_num, r_order, MAX(vendor) AS vendor -- etc.
FROM
  (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date
    FROM Parts.dbo.po as p INNER JOIN
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar)
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date
  ) as tbl
GROUP BY r_num, r_order