mysql - 滞后函数中组函数的使用无效

Question

我是 SQL 新手，有一个相当简单的查询，但在尝试使用它时，我不断收到错误“无效使用组函数”。这是我的查询:

select CreateDate as date,
 count(*) as count,
 lag(count(*), 1) OVER (order by CreateDate) as Previous 
from contacts

有人可以解释为什么这不起作用以及如何让它正常运行吗？

Answer 1

您的查询引发错误消息:

ER_MIX_OF_GROUP_FUNC_AND_FIELDS: In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column 'test.contacts.createdate'; this is incompatible with sql_mode=only_full_group_by

这与lag()无关。您的查询只是缺少 group by 子句:

select 
    CreateDate as date,
    count(*) as count,
    lag(count(*), 1) over(order by CreateDate) as previous 
from contacts
group by createdate