如何计算SQL中的平均值？

Question

lets say I have the following table:

**FOOD**  | **AMOUNT**
  Bread   |   2
  Banana  |   5
  Pizza   |   4
  Apple   |   57
  Mandarin|   9
  Orange  |   8

Final result:

  Bread  |  Percentage Of Total
  Banana |  percentage of total

etc etc

I tried it in every single way, but couldn't find a solution. I hope someone can help me.

Answer 1

Using ANSI SQL (and SQL Server supports this syntax), you can do:

select food, sum(amount),
       sum(amount) / sum(sum(amount)) over () as proportion_of_total
from t
group by food;

Note: Some databases do integer division, so you may need to convert to a floating point or fixed point type.

Answer 2

We can also try like below-

DECLARE @tbl AS TABLE 
(
     food VARCHAR(15)
    ,amount INT
)

INSERT INTO @tbl VALUES
('bread', 2)
,('banana', 5)
,('pizza', 4)
,('apple', 57)
,('mandarin', 9)
,('orange', 8)

SELECT
    DISTINCT 
     food
    ,SUM(amount) OVER() TotalAmount
    ,SUM(amount) OVER (PARTITION BY food) PerFoodTotal
    ,CAST(SUM(amount) OVER (PARTITION BY food) * 100. / (SUM(amount) OVER()) AS DECIMAL(10,2)) [Percentage Of Total]
FROM @tbl

OUTPUT

food            TotalAmount PerFoodTotal Percentage Of Total
--------------- ----------- ------------ ---------------------------------------
apple           85          57           67.06
banana          85          5            5.88
bread           85          2            2.35
mandarin        85          9            10.59
orange          85          8            9.41
pizza           85          4            4.71

(6 row(s) affected)

Answer 3

You can try something like this:

declare @tbl as table (
    food varchar(15)
    ,amount int
)

insert into @tbl values
('bread', 2)
,('banana', 5)
,('pizza', 4)
,('apple', 57)
,('mandarin', 9)
,('orange', 8)


select SUM(amount) from @tbl


select
    food
    ,SUM(amount) as [food amount]
    ,(SUM(cast(amount as numeric(18,2))) / (select sum(cast(amount as numeric(18,2))) from @tbl)) * 100  as [Percentage Of Total]
    ,(select sum(amount) from @tbl) as total
from @tbl
group by food

Answer 4

Here you got a way fo getting the PercentageOfTotal, asuming that the sum of all will not be 0

DECLARE @total INT = (SELECT SUM(AMOUNT) FROM Table1)

SELECT FOOD, CAST((CAST((100 * AMOUNT) AS DECIMAL (18,2)) / @total  ) AS DECIMAL(18,2)) AS PercentageOfTotal from Table1

Answer 5

SQL Fiddle

MS SQL Server 2014 Schema Setup :

CREATE TABLE MusicGenres (name varchar(10)) ;
INSERT INTO MusicGenres (name)
VALUES ('Pop'),('Techno'),('Trance'),('trap'),('Hardcore'),('Electro') ;

CREATE TABLE Table2 (SongID int, MusicGenres varchar(10)) ;
INSERT INTO Table2 (SongID, MusicGenres)
VALUES (1,'Hardcore')
   ,(2,'Hardcore')
   ,(3,'Pop')
   ,(4,'Trap')
   ,(5,'Hardcore')
   ,(6,'Pop')
   ,(7,'Electro')
   ,(8,'Electro')
   ,(9,'Pop')
   ,(10,'Pop')
   ,(11,'Pop')
 ;

Query 1 :

SELECT s1.name
  , s1.recCount
  , ( s1.recCount / CAST( ( SUM(recCount) OVER() ) AS decimal(5,2) ) )*100  AS pct
FROM (
    SELECT m.name
      , count(t.SongID) AS recCount
    FROM MusicGenres m
    LEFT OUTER JOIN Table2 t ON m.name = t.MusicGenres
    GROUP BY m.name
) s1

Could be shortened to

SELECT m.name
  , count(t.SongID) AS recCount
  , ( count(t.SongID) / CAST( ( SUM(count(t.SongID)) OVER() ) AS decimal(5,2) ) 
)*100  AS pct
FROM MusicGenres m
LEFT OUTER JOIN Table2 t ON m.name = t.MusicGenres
GROUP BY m.name

Results :

|     name | recCount |     pct |
|----------|----------|---------|
|  Electro |        2 | 18.1818 |
| Hardcore |        3 | 27.2727 |
|      Pop |        5 | 45.4545 |
|   Techno |        0 |       0 |
|   Trance |        0 |       0 |
|     trap |        1 |  9.0909 |