mySQL：我可以添加一个计算列，其中包含具有相同共享值的所有其他行的总和吗

Question

I have a data set where each record includes street, zipcode, city, population. I want to find (% of population one zipcode is to the entire city's population) but can't figure out how to group by zip and then add a column that shows total city's population for every zip with that same city.

[Ex Trying to find (Sum_of_City and Percent_of_City)]

Code I tried:

SELECT
   city,
   zipcode,
   sum(population) as Pop_Count_ (
   SELECT
      SUM(zSUM) 
   FROM
      (
         SELECT
            SUM(Distinct zipcode) AS zCount 
         FROM
            myTable 
         GROUP BY
            city
      )
      AS A)_ 
   FROM
      myTable_ 
   GROUP BY
      city,
      zipcode;

Answer 1

Use window functions:

select city, zipcode, sum(population) as population,
       sum(population) / sum(sum(population)) over (partition by city) as zipcode_ratio
from t
group by city, zipcode;

Answer 2

In case you're not on MySQL 8 (in which case you can't use Window Functions) , here's an alternative approach... Aggregate twice, then Join...

SELECT
  city_zip.city, city_zip.zip_code, city_zip.popluation, city_zip.poupluation / city.population AS ratio
FROM
(
    SELECT city, zipcode, sum(population) AS population
      FROM myTable
  GROUP BY city, zip_code
)
  AS city_zip
INNER JOIN
(
    SELECT city, sum(population) AS population
      FROM myTable
  GROUP BY city
)
  AS city
    ON city.city = city_zip.city

Or, using a correlated-subquery...

SELECT
  city,
  zip_code,
  SUM(popluation),
  SUM(population)
  /
  (
    SELECT SUM(population)
      FROM myTable AS city
     WHERE city.city = city_zip.city
  )
FROM
  myTable AS city_zip
GROUP BY
  city,
  zip_code

I suspect the longer code might be faster, though I'm not entirely sure.