VARCHAR上的INNER JOIN

Question

以下查詢返回0行，即使這兩個表包含多個匹配值。

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

因爲isrc列是varchar類型，所以我懷疑它可能是表格排序問題。但是，將這兩種排序方式更改爲utf-8並沒有解決問題。

這裏有什麼問題？

Answer 1

試試下面，

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

注：

1. 修剪兩側的值
2. 規範化的情況下

Answer 2

在看看你認爲是matc每個表興值：

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，你可能會發現有用的摘要：

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並且是同爲一個比較的語義可能不相同（最後的空格會影響group by的相似性，但不應影響相似性）。但是，這會讓你知道在兩個表中可以匹配什麼。