两列中的Oracle SQL公共条目

Question

我有一个包含两列常用条目的表。

例如：

Column1    Column2
Entry1  || NULL  
Entry2  || Entry1
Entry3  || Entry1
Entry4  || Entry4
Entry5  || NULL

我想查找第1列的条目出现在第2列的次数。

所以结果会是这样的：

Column1    Count
Entry1  || 2
Entry2  || 0
Entry3  || 0
Entry4  || 1
Entry5  || 0

Answer 1

WITH counts AS (
    SELECT column2, COUNT(*) AS the_count
      FROM x
      GROUP BY column2
)
SELECT x.column1, COALESCE(c.the_count, 0)
  FROM x LEFT OUTER JOIN counts c ON (x.column1 = c.column2)
  ORDER BY 1