VARCHAR上的INNER JOIN

Question

以下查询返回0行，即使这两个表包含多个匹配值。

SELECT i.isrc, m.isrc FROM table1 i INNER JOIN table2 m ON i.isrc = m.isrc; 

因为isrc列是varchar类型，所以我怀疑它可能是表格排序问题。但是，将这两种排序方式更改为utf-8并没有解决问题。

这里有什么问题？

Answer 1

试试下面，

SELECT i.isrc, m.isrc 
FROM table1 i 
INNER JOIN table2 m 
ON UPPER(TRIM(i.isrc)) = UPPER(TRIM(m.isrc)) 

注：

1. 修剪两侧的值
2. 规范化的情况下

Answer 2

在看看你认为是matc每个表兴值：

select src, sum(in1) as in1, sum(in2) as in2 
from ((select distinct i.isrc as src, 1 as in1, 0 as in2 from table1 i) union all 
     (select distinct m.isrc as src, 0 as in1, 1 as in2 from table1 m) 
    ) t 
group by src; 

做上述前，你可能会发现有用的摘要：

select in1, in2, count(*), min(src), max(src) 
from (select src, sum(in1) as in1, sum(in2) as in2 
     from ((select distinct i.isrc as src, 1 as in1, 0 as in2 from table1 i) union all 
      (select distinct m.isrc as src, 0 as in1, 1 as in2 from table1 m) 
      ) t 
     group by src 
    ) s 
group by in1, in2; 

的是相同的group by并且是同为一个比较的语义可能不相同（最后的空格会影响group by的相似性，但不应影响相似性）。但是，这会让你知道在两个表中可以匹配什么。