sql - Oracle Count in Group by -

for example ,i have table represents teachers in school including his/her name , sex , class he/she belongs to.i want know , each class, how many males , how many females teachers in sql statement.

abosolutely , each teacher can belong 1 class!

column  type       description class   number     class number,e.g. 0,1,2,3 ... sex     number     teacher sex, 0 represents male , 1 represents female. teacher varchar    teacher name lily,lucy 

more deep:

i have table represents teachers in school including his/her name , age , class he/she belongs to.i want know , each class, how many teachers younger 20 , how many teachers older 20 @ same time in sql statement.

column  type       description class   number     class number,e.g. 0,1,2,3 ... age     number     teacher ages. teacher varchar    teacher name lily,lucy 

try :

select class, sum(male) male, sum(female) female, sum(younger) younger, sum(older) older from( select class, (case when sex = 0 1 else 0 end) male, (case when sex = 1 1 else 0 end) female, (case when age < 20 1 else 0 end) younger, (case when age >= 20 1 else 0 end) older yourtable ) t group class