Question

我有这些表 - 书（b），贸易（t），TradingDesk（d），CounterParty（c）。

Trade（t）有2列买方，卖方看起来像

**Buyer** **Seller**
B456  B222 
C55   B222 
B323  C4333

我必须根据买方和卖方列中的值加入书（b）。即，如果值以'B'开头，则应检查Books表中是否存在该ID，例如：对于B456 - 应使用Books表检查id 456。

我写了以下内容可以做到这一点：

SELECT DISTINCT d.Name, t.Buyer, t.Seller FROM  Book AS b
  INNER JOIN TradingDesk AS d  ON b.TradingDeskId = d.Id
    Join Trade as t 
       on  substring(t.Seller,2,len(t.Seller)) = cast(b.Id as varchar)
UNION
SELECT DISTINCT d.Name , t.Buyer, t.Seller FROM  Book AS b 
  INNER JOIN TradingDesk AS d ON b.TradingDeskId = d.Id
    Join Trade as t 
       on substring(t.Buyer,2,len(t.Buyer)) = cast(b.Id as varchar)

现在，我需要使用CounterParty（c）表检查以'C'开头的值。我尝试在连接中添加where条件，但这不起作用并在where语句中给出错误。我尝试用条件调整连接条件：

on  substring(t.Seller,2,len(t.Seller)) = cast(b.Id as varchar) where t.Seller like 'B%' 
 AND
substring(t.Seller,2,len(t.Seller)) = cast(c.partyId as varchar) where t.Seller like 'C%'

但似乎我不能在ON部分设置两个条件，其中多个条件。

实现这一目标的任何方式？

由于摩尼

Answer 1

将其转换为LEFT JOIN，然后将附加条件放在那里

SELECT DISTINCT d.Name, t.Buyer, t.Seller FROM  Book AS b
  LEFT JOIN TradingDesk AS d  ON b.TradingDeskId = d.Id
    LEFT Join Trade as t 
       on  substring(t.Seller,2,len(t.Seller)) = cast(b.Id as varchar)

       AND t.Seller like 'B%' -- put your additional condition(s) here

UNION
SELECT DISTINCT d.Name , t.Buyer, t.Seller FROM  Book AS b 
  LEFT JOIN TradingDesk AS d ON b.TradingDeskId = d.Id
    LEFT Join Trade as t 
       on substring(t.Buyer,2,len(t.Buyer)) = cast(b.Id as varchar)

Answer 2

以下查询很可能是次优的，但它应该为您提供必要的结果，因此，至少为您提供一个起点：

SELECT
  d.Name,
  t.Buyer,
  t.Seller
FROM (
  SELECT
    'B' AS Prefix,
    COUNT(Id AS varchar(20)) AS Id,
    TradingDeskId
  FROM Book
  UNION ALL
  SELECT
    'C' AS Prefix,
    COUNT(Id AS varchar(20)) AS Id,
    TradingDeskId
  FROM CounterParty
) bc
  INNER JOIN TradingDesk d ON d.Id = bc.TradingDeskId
  INNER JOIN Trade t ON bc.Prefix + bc.Id IN (t.Buyer, t.Seller)

Answer 3

你可以这样做（未经测试）：

select 
  t.Buyer, 
  t.Seller, 
  case when t.Buyer like 'B%' THEN (select BookName from Book where BookId = t.Buyer)
                              ELSE (select CpName from Counterparty where CPId = t.Buyer)
  end BuyerName,
  case when t.Seller like 'B%' THEN (select BookName from Book where BookId = t.Seller)
                               ELSE (select CpName from Counterparty where CPId = t.Seller)
  end SellerName
from 
  Trade t

您遇到的问题是，由于您要加入的表是数据驱动的，因此您无法在FROM子句中指定它。

SQL查询帮助 - 在连接条件中有两个条件

3 个答案: