postgresql - Sort by aggregate value in sql -


let's have following student data:

classroom     gender  student_id ------------------------------------- first grade   m       123 first grade   f       124 first grade   f       125 second grade  m       126 third grade   m       127 ...

i want produce following result: top 3 biggest classrooms ordered total number of students detail each:

classroom          boys_count  girls_count  total_count -------------------------------------------------- third grade        30          30           60 first grade        20          5            25 fourth grade       10          10           20

how can in sql ? if necessary, can use specific postrges features.

what tried far:

select count(*) total_count   , gender   , classroom order 1 group classroom, gender limit 3

then re-organise results in scripting language. slow. want have correct results 1 query

select classroom name,        sum(case when gender = 'm' 1 else 0 end) boys_count,        sum(case when gender = 'f' 1 else 0 end) girls_count,        count(*) total_count your_table group classroom order count(*) desc limit 3

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