Postgres 13

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CREATE TABLE stop_and_searches(
  sas_id bigserial PRIMARY KEY
, officer_defined_ethnicity text
, object_of_search text
, outcome text
);
INSERT INTO stop_and_searches VALUES
  (1, 'ethnicity1', 'Psychoactive substances', 'Arrest')
, (2, 'ethnicity1', 'Dog', 'Arrest')
, (3, 'ethnicity2', 'Stolen goods', 'A no further action disposal')
, (4, 'ethnicity3', 'Firearms', 'Arrest')
, (5, 'ethnicity1', 'Fireworks', 'A no further action disposal')
, (6, 'ethnicity2', 'Firearms', 'Arrest')
, (7, 'ethnicity3', 'Fireworks', 'Arrest')
, (8, 'ethnicity1', 'Firearms', 'A no further action disposal')
, (9, 'ethnicity2', 'Stolen goods', 'Arrest')
, (10, 'ethnicity1', 'Cat', 'Arrest')
;
10 rows affected

SELECT DISTINCT ON (1)
       officer_defined_ethnicity, object_of_search, count(*) AS ct
FROM   stop_and_searches
GROUP  BY 1, 2
ORDER  BY 1, 3 DESC, 2;


officer_defined_ethnicity
object_of_search
ct


ethnicity1
Cat
1

ethnicity2
Stolen goods
2

ethnicity3
Firearms
1


-- more explicitly:
SELECT DISTINCT ON (officer_defined_ethnicity)
       officer_defined_ethnicity, object_of_search, count(*) AS ct
FROM   stop_and_searches
GROUP  BY officer_defined_ethnicity, object_of_search
ORDER  BY officer_defined_ethnicity, ct DESC, object_of_search;


officer_defined_ethnicity
object_of_search
ct


ethnicity1
Cat
1

ethnicity2
Stolen goods
2

ethnicity3
Firearms
1