Calculate the variance of the weights of all players [closed] - sql

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We are given data from nba where a description of each table is as follows:
coaches_season, each tuple of which describes the performance of one coach in one season;[cid, year, yr_order, year, season_win, season_loss, play_off_win, play_off_loss, tid]
teams, each tuple of which gives the basic information of a team; [tid, location, name, league]
players, each tuple of which gives the basic information of one player; [ilkid, firstname, lastname, position, first_season, last_season, h_feet, h_inches, weight, college, birthday]
player_rs, each tuple of which gives the detailed performance of one player in one regular season; [ilkid,tid, pts, asts, of, ftm, tpa,tpm, fgm,fga, fta, blk, turnover, stl, dreb, oreb, reb, minutes, gp, league, lastname, firstname, year]
player_rs_career, each tuple of which gives the detailed regular-season performance of one player in his career;[ilkid, firstname, lastname, fga, fgm, fta, ftm, tpa, tpm, pf, stl, oreb, minutes, gp, dreb, asts, turnover, blk, reb, league]
draft, each tuple of which shows the information of an NBA draft. [draft_year, firstname, lastname, draft_round, tid, selection, draft_from, ilkid, league]
I found many queries but am stuck with these 3 queries:
I) For each college, print the college name and average number of drafts (per season) they sent to NBA. However, only report those colleges that sent drafts in at least 3 seasons.
II) Calculate the variance of the weights of all players;
III) Print the first and last names of those who either scored more than 12000 points in their careers or played for more than 12 seasons.

Answer 1

In this case especially the DDL for each table including Primary and Foreign Key definitions. Also include sample data, as text, not an image and the expected output from that data. Further, in this case you may want to include the definitions for the column names as not everyone is familiar with the acronyms used for the NBA.
With that said, I'll give it a stab. Note since you didn't include test data nor table definitions the queries have NOT been tested.
-- I) For each college, print the college name and average number of drafts (per season) they sent to NBA.
-- However, only report those colleges that sent drafts in at least 3 seasons.
-- assumptions:
-- draft yr integer specifying calendar year of draft
-- draft_from text name of college
-- average number of drafts (per season) ?? how many drafts are there per season
-- what is the difference between season and year
with draft as
(select max(draft_yr) dy from draft_year)
, dy_last3 as
(select distinct draft_from df
from draft_year
where exists (select null from draft_year, draft where draft_yr = dy)
and exists (select null from draft_year, draft where draft_yr = dy-1)
and exists (select null from draft_year, draft where draft_yr = dy-2)
)
select draft_from, round(avg(drc),2) adv_drafts
from (
select draft_from, draft_yr, count(*) drc
from draft_year
where draft_from in (select df from dy_last3)
group by draft_from,draft_yr
) t
group by draft_from;
-- II) Calculate the variance of the weights of all players;
-- assumption: weight defined as float;
select var_samp(weight) from player;
OR
select var_pop(weight) from player;
-- III)Print the first and last names of those who either scored more than 12000 points in their careers or played for more than 12 seasons.
-- assumption fgm => field goals made = 2 points each
-- ftm => free throws made = 1 point each
-- tpm => 3 point shot make = 3 points each
-- ilkid => Pk in player and FK in player_rs_career
-- table player_rs_career does include last/current season
-- note player_rs_career does NOT contain year/season, unless hidden by undescribed column name
select distinct *
from (select p.firstname, p.lastname
, sum(ftm + (2*fgm) + (3*tpm)) over (partition by p.ilkid) points
, (coalesce (p.last_season, extract (year from now())::integer) - p.first_season + 1) seasons
from player p
join player_rs_career pc
on p.ilkid = pc.ilkid
) pp
where points > 12000
or seasons > 12;