MariaDB 10.9

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CREATE TABLE test (date_ DATE, count INT);
insert into test values ("2023-01-01", 10);
insert into test values ("2023-01-01", 17);
insert into test values ("2023-01-01", 20);
insert into test values ("2023-02-01", 13);
insert into test values ("2023-02-01", 13);
insert into test values ("2023-02-01", 14);
select distinct date_, 
  percentile_cont(0.5) WITHIN GROUP (ORDER BY count) OVER (PARTITION BY date_) AS p50
from test


date_
p50


2023-01-01
17.0000000000

2023-02-01
13.0000000000