根据Null或Not Null值删除重复项

Question

我有一张表，其中有重复记录，包含以下属性：

1. Primary_ID
2. 评论

现在的问题是，存在具有相同主键但不同“注释”的重复记录。 记录存在如下：

+------------+-----------+
| Primary_ID | Comments  |
+------------+-----------+
|          1 | abc       |
|          1 | null      |
|          1 | abc       |
|          2 | asdf      |
|          3 | null      |
|          4 | abc       |
|          4 | null      |
+------------+-----------+

我希望查询删除具有重复项且注释为空的记录。 这是它应该是什么样子：

+------------+----------+
| Primary_ID | Comments |
+------------+----------+
|          1 | abc      |
|          2 | asdf     |
|          3 | null     |
|          4 | abc      |
+------------+----------+

我尝试使用以下查询完成此操作：

delete from myTab
  where PRIMARY_ID 
    not in
    ( SELECT distinct PRIMARY_ID, COMMENT 
    FROM myTab)

Answer 1

DELETE FROM myTab
WHERE Comments IS NULL 
      OR PRIMARY_ID NOT IN(SELECT PRIMARY_ID
                            FROM myTab
                            HAVING COUNT(PRIMARY_ID)>1)

修改

将OR替换为AND，因为它取决于你的意思删除有重复的记录并且评论为nul