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How to solve the problem of group statistics in MySQL database

Author：Eve Cole Update Time：2009-05-30 23:59:16
First prepare four tables A, B, C, and D. 

--------------------------------     
  A | B | C | D     
  ab | ac | ad | de 1 1 | 1 1 | 1 A | A 1     
  2 2 | 1 3 | 2 B | B 2     
  3 4 | 1 4 | 3 C | C 3     
  4 6 | 2 1 | 4 D | D 4     
  --------------------------------

Next we need to use a sql statement to count all the columns of table A, table B and the columns associated with the a field of table A, and associate table D with table A through table C. The results obtained are as follows:

 

1 1 3 1     
  2 2 1 2     
  3 4 0 3     
  4 6 0 4

Mysql statement solution:

 

select Aa,Ab,IFNULL(c,0) as c,Da 
from (select 1 as a,2 as b union all
select 2 as a,2 as b union all
select 3 as a,4 as b union all
select 4 as a,6 as b) as A 
left outer join     
(select a,count(a) as c from(
select 1 as a,3 as c union all
select 1 as a,3 as c union all
select 1 as a,3 as c union all
select 2 as a,3 as c ) B group by a) as B
onAa=Ba 
join 
(select 1 as a,'A' as d union all
select 2 as a,'B' as d union all
select 3 as a,'C' as d union all
select 4 as a,'D' as d ) as C 
onAa=Ca 
join(select 1 as a,'A' as d union all
select 2 as a,'B' as d union all
select 3 as a,'C' as d union all
select 4 as a,'D' as d ) as D
on Dd=Cd
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