Select 从 MySQL 表中每年最多 1 条记录

Question

I need to extract data from a MySQL table, but am not allowed to include a record if there's a previous record less than a year old.

Given the following records, only the records 1 , 3 and 5 should be included (because record 2 was created 1 month after record 1, and record 4 was created 1 month after record 3):

1   2019-12-21
2   2020-01-21
3   2021-12-21
4   2022-01-21
5   2023-12-21

I came up with the following non-functional solution:

SELECT 
    * 
FROM 
    table t 
WHERE 
    (created_at > DATE_ADD(
        (SELECT 
            created_at 
        FROM 
            table t2 
        WHERE 
            t2.created_at < t.created_at 
        ORDER BY 
            t2.created_at 
        DESC LIMIT 1), INTERVAL 1 YEAR)

But this only returns the first and the last record, but not the third:

1   2019-12-21
5   2023-12-21

I know why: the third record gets excluded because record 2 is less than a year old. But record 2 shouldn't be taken into account, because it won't make the list itself.

How can I solve this?

Answer 1

Using lag , assuming your MySql supports it, you can calculate the difference in months using period_diff

with d as (
  select * , 
    period_diff(extract(year_month FROM date),
      extract(year_month from lag(date,1,date) over (order by date))
    ) as m
  from t
 )
 select id, date
 from d
 where m=0 or m>12

Demo Fiddle