根据多个条件连接两个表

Question

我有两个表产品和职位。

产品：

id BIGINT PRIMARY KEY,
product VARCHAR(100),
criterium1 VARCHAR(100),
criterium2 VARCHAR(100)

职位：

id BIGINT PRIMARY KEY,
position VARCHAR(100),
criterium1 VARCHAR(100),
criterium2 VARCHAR(100)

每个表都有criterium1和criterium2。我想要一个包含职位和产品之间连接的结果集。对于每个职位，我都想要与 criterium1 或 criterium2 匹配的相应产品；当 criterium1 找不到或为 NULL 时，它需要在 criterium2 上匹配。

SQL 语句会是什么样的？

到目前为止，我已经尝试过：

SELECT * FROM positions pos 
INNER JOIN products pro 
ON COALESCE(pos.criterium1, pos.criterium2,'') 
    = COALESCE( pro.criterium1, pro.criterium2,'') 

然而，这不匹配pro.criterium1到pos.criterium1或pro.criterium2到pos.criterium2。

补充：对不起，我的要求有点模糊。让我试着完成这幅画。

我们使用的是 SQL Server 2005。

products:

id   product   criterium1   criterium2
 1    pro1       AAA1         910
 2    pro2       106          BB2
 3    pro3       AB1          XXY

positions:

id  position  criterium1  criterium2
 1    pos1       NULL         910
 2    pos2       106          CCC
 3    pos3       XXX          BB2
 4    pos4       AA1          XXY
 5    pos5       NULL         123

我正在寻找的是使用条件匹配的表格连接，我想将位置与产品相匹配。首先我想匹配criterium1。如果我在 criterium1 上找不到匹配项或位置 criterium1 为 NULL，我需要在 criterium2 上匹配。

在上面的例子中，预期的结果集是：

resultset
positionId  productId
 1            1 (no match on criterium1 since NULL, match on criterium2 )
 2            2 (match on criterium1)
 3            2 (no match on criterium1, match on criterium2 )
 4            1 (match on criterium1, criterium2 match is disregarded)

我只想匹配positions.criterium1与products.criterium1和positions.criterium2使用products.criterium2。

Answer 1

假设 pro1，criterium1 应该是 AA1，这会产生您正在寻找的结果：

SELECT pos.id, pro.id, pos.criterium1, pos.criterium2
   , pro.criterium1, pro.criterium2 
FROM Positions pos
JOIN Products pro ON pos.criterium1 = pro.criterium1 
   OR (pos.criterium2 = pro.criterium2
   AND pos.id NOT IN (
      SELECT posx.id FROM Positions posx
      JOIN Products prox ON posx.criterium1 = prox.criterium1
   ))
ORDER BY 1;

测试查询（仅在 Oracle 中测试）：

WITH Products AS (
   SELECT 1 id, 'AA1' criterium1, '910' criterium2 FROM dual UNION ALL
   SELECT 2 id, '106'  criterium1, 'BB2' criterium2 FROM dual UNION ALL
   SELECT 3 id, 'AB1'  criterium1, 'XXY' criterium2 FROM dual
   ),
   Positions AS (
   SELECT 1 id, NULL  criterium1, '910' criterium2 FROM dual UNION ALL
   SELECT 2 id, '106' criterium1, 'CCC' criterium2 FROM dual UNION ALL 
   SELECT 3 id, 'XXX' criterium1, 'BB2' criterium2 FROM dual UNION ALL 
   SELECT 4 id, 'AA1' criterium1, 'XXY' criterium2 FROM dual UNION ALL 
   SELECT 5 id, NULL  criterium1, '123' criterium2 FROM dual    
   )   
SELECT pos.id, pro.id, pos.criterium1, pos.criterium2
   , pro.criterium1, pro.criterium2 
FROM Positions pos
JOIN Products pro ON pos.criterium1 = pro.criterium1 
   OR (pos.criterium2 = pro.criterium2
   AND pos.id NOT IN (
      SELECT posx.id FROM Positions posx
      JOIN Products prox ON posx.criterium1 = prox.criterium1
   ))
ORDER BY 1;