MySQL 8.0

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create table test (
  code1 varchar(20)
, code2 varchar(20)
, value integer
  )
insert into test (code1, code2, value) values
  ('a','x',100)
, ('a','y',200)
, ('a','z',300)

Records: 3  Duplicates: 0  Warnings: 0


SELECT @@sql_mode;


@@sql_mode


ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION


SET SESSION sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
select
     *
   , sum(value)
from test
group by
     code1


code1
code2
value
sum(value)


a
x
100
600


SET SESSION sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
select
     *
   , sum(value)
from test
group by
     code1

Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'fiddle.test.code2' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by


select
     code1
   , sum(value)
from test
group by
     code1


code1
sum(value)


a
600