MySQL：使用分组依据选择并除以计数

Question

Here's a data set of my table

ID  |groupID|   Start   | End   | SegStart  | SegEnd    | something
-------------------------------------------------------------------
1   |   1   |   0.234   | 0.345 |   0.345   |   0.677   | 0
2   |   1   |   0.234   | 0.345 |   0.346   |   0.678   | 0
3   |   1   |   0.234   | 0.345 |   0.347   |   0.679   | 0
4   |   1   |   0.234   | 0.345 |   0.348   |   0.680   | 1
5   |   2   |   0.345   | 0.567 |   0.568   |   0.570   | 0
6   |   2   |   0.345   | 0.567 |   0.569   |   0.571   | 1
7   |   3   |   0.567   | 0.678 |   0.679   |   0.681   | 0
8   |   3   |   0.567   | 0.678 |   0.680   |   0.682   | 0
9   |   3   |   0.567   | 0.678 |   0.681   |   0.683   | 1

I want to calculate a value from the Start / End columns as well as the SegStart / SegEnd columns where something = "1" and then divide this value by the number of items in a group (group 1 has 4 items, group 2 has 2, group 3 has 3, etc)

I've tried this query, but it gives me the error "Subquery returns more than 1 row"

select (((End - Start) - (SegEnd - SegStart)) / 
  (select count(*) as NumSeg from table group by groupID)) as NewValue 
from table where something = "1"; 

I would like a list of the new value for each group, kind of like this (values are imaginary):

groupID |   NewValue
--------------------
1       |   0.102
2       |   0.110   
3       |   0.036

Answer 1

You could try this:

CREATE TABLE mytable(
   ID        INTEGER  NOT NULL PRIMARY KEY 
  ,groupID   INTEGER  NOT NULL
  ,Start     NUMERIC(11,3) NOT NULL
  ,End       NUMERIC(7,3) NOT NULL
  ,SegStart  NUMERIC(11,3) NOT NULL
  ,SegEnd    NUMERIC(11,3) NOT NULL
  ,something BIT  NOT NULL
);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (1,1,0.234,0.345,0.345,0.677,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (2,1,0.234,0.345,0.346,0.678,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (3,1,0.234,0.345,0.347,0.679,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (4,1,0.234,0.345,0.348,0.680,1);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (5,2,0.345,0.567,0.568,0.570,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (6,2,0.345,0.567,0.569,0.571,1);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (7,3,0.567,0.678,0.679,0.681,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (8,3,0.567,0.678,0.680,0.682,0);
INSERT INTO mytable(ID,groupID,Start,End,SegStart,SegEnd,something) VALUES (9,3,0.567,0.678,0.681,0.683,1);


select A.GROUPID, ((End - Start) - (SegEnd - SegStart)) / B.NumSeg AS V1
from mytable A
INNER JOIN  (select GROUPID, count(*) as NumSeg from mytable group by GROUPID) B ON A.GROUPID = B.GROUPID
where something = "1"; 

Output:

    GROUPID V1
1   1   -0,0552500
2   2   0,1100000
3   3   0,0363333