Mysql 查询,仅当其所有记录在特定列中都为null时才返回true
假设有一个表赋值,其列为Mysql 查询,仅当其所有记录在特定列中都为null时才返回true,mysql,sql,count,having-clause,sql-null,Mysql,Sql,Count,Having Clause,Sql Null,假设有一个表赋值,其列为 分配id 转让人 任务id 受让人 同一任务id可由指派人指派给1个以上的指派人。 目前,我有一个任务分配给2个工作人员。让我们看看下表中的示例: +---------------+----------+---------+----------+ | assignment_id | assignor | task_id | assignee | +---------------+--------------------+----------+ | 1
- 分配id
- 转让人
- 任务id
- 受让人
+---------------+----------+---------+----------+
| assignment_id | assignor | task_id | assignee |
+---------------+--------------------+----------+
| 1 | a1 | t1 | x1 |
+---------------+----------+---------+----------+
| 2 | a1 | t1 | x2 |
+---------------+----------+---------+----------+
当转让人删除受让人时,该表如下所示:
+---------------+----------+---------+----------+
| assignment_id | assignor | task_id | assignee |
+---------------+--------------------+----------+
| 1 | a1 | t1 | x1 |
+---------------+----------+---------+----------+
| 2 | a1 | t1 | null |
+---------------+----------+---------+----------+
现在,我需要一个查询,该查询仅当此特定任务id的每个记录在列中都有null值时才返回true。
到目前为止,我写的是:
SELECT DISTINCT task_id, nulls, total,
(CASE
WHEN nulls = total then true
ELSE false
END) unassigned
FROM
(
SELECT task_id,
(SELECT count(*) FROM assignments b WHERE assignee IS NULL AND b.task_id = a.task_id) 'nulls',
(SELECT count(*) FROM assignments b WHERE b.task_id = a.task_id) 'total'
FROM assignments a
WHERE assignee is NULL) c
结果是:
+--------------------------------------+
| task_id | nulls | total | unassigned |
+--------------------------------------+
| 1 | 2 | 2 | 1 |
+---------+-------+-------+------------+
对改进我的查询或完全替换它有什么建议吗?如果我没有弄错,您可以使用聚合:
select assignment_id,
count(*) - count(assignee) as nulls,
count(*) as total,
case when count(assignee) = 0 then 1 else 0 end as unassigned
from assignments
group by assignment_id
如果要筛选未分配的分配,则可以在查询末尾添加having
子句:
having count(assignee) = 0
我认为您只需要两列:
task\u id
和assignment
中null
s的行数因此,
按taskid分组
,并在having
子句中设置条件:
select task_id, count(*) total
from assignments
group by task_id
having max(assignee) is null
条件的max(assignment)为null
只返回assignee
列中只有null
s的taskid
s