MariaDB [mart]> SELECT last_name, year(date_of_birth) FROM efis_people LIMIT 5;
+-----------+---------------------+
| last_name | year(date_of_birth) |
+-----------+---------------------+
| Aadamsoo  |                1975 |
| Aaloe     |                1944 |
| Aamisepp  |                NULL |
| Aanja     |                NULL |
| Aanja     |                NULL |
+-----------+---------------------+


MariaDB [mart]> SELECT DISTINCT classificator_code FROM efis_film_role_person;
+--------------------+
| classificator_code |
+--------------------+
| FILM_ROLE_MAIN     |
| FILM_ROLE_SIDE     |
| FILM_ROLE_EPISODE  |
+--------------------+

SELECT YEAR(date_of_birth) FROM efis_people 
  JOIN efis_film_role_person ON 
     efis_film_role_person.people_id=efis_people.id
  WHERE classificator_code='FILM_ROLE_MAIN'
  AND NOT YEAR(date_of_birth) IS NULL;
  
SELECT YEAR(date_of_birth) FROM efis_people 
  JOIN efis_film_role_person ON 
     efis_film_role_person.people_id=efis_people.id
  WHERE classificator_code='FILM_ROLE_SIDE'
  AND NOT YEAR(date_of_birth) IS NULL;
  
SELECT AVG(YEAR(date_of_birth)) FROM efis_people 
  JOIN efis_film_role_person ON 
     efis_film_role_person.people_id=efis_people.id
  WHERE classificator_code='FILM_ROLE_SIDE'
  AND NOT YEAR(date_of_birth) IS NULL;

 
library(RMySQL)
yhendus<-dbConnect(dbDriver("MySQL"), user='mart', password='ajutine1234', host='localhost', dbname='mart' )
paring<-dbSendQuery(yhendus, "
 SELECT YEAR(date_of_birth) AS synniaasta FROM efis_people 
  JOIN efis_film_role_person ON 
     efis_film_role_person.people_id=efis_people.id
  WHERE classificator_code='FILM_ROLE_MAIN'
  AND NOT YEAR(date_of_birth) IS NULL")
andmed=fetch(paring, n=-1)
#print(andmed$synniaasta)
paring<-dbSendQuery(yhendus, "
 SELECT YEAR(date_of_birth) AS synniaasta FROM efis_people 
  JOIN efis_film_role_person ON 
     efis_film_role_person.people_id=efis_people.id
  WHERE classificator_code='FILM_ROLE_SIDE'
  AND NOT YEAR(date_of_birth) IS NULL")
andmed2=fetch(paring, n=-1)
#print(andmed2$synniaasta)
t.test(andmed$synniaasta, andmed2$synniaasta) 
 
data:  andmed$synniaasta and andmed2$synniaasta
t = 2.2874, df = 8786, p-value = 0.0222
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 0.1537264 1.9960063
sample estimates:
mean of x mean of y
 1950.466  1949.391