For triggers INDEX_STATISTICS.QUERIES only counts the triggering query

SET @userstat.save= @@userstat;

set global userstat= 1;

create or replace table t1 (a int, key(a));

insert into t1 values (1),(2),(3),(4),(1);

create or replace table t2 (b int);

create trigger tr before insert on t2 for each row set new.b = (select count(*) from t1 where a = new.b);

flush index_statistics;

insert into t2 values (1),(2),(3),(4),(5);

show index_statistics;

# Cleanup

set global userstat= @userstat.save;

drop table t1, t2;

flush index_statistics;

insert into t2 values (1),(2),(3),(4),(5);

show index_statistics;

Table_schema	Table_name	Index_name	Rows_read	Queries

test	t1	a	5	1