情況下用mysql

Question

我有3列doc_date，chem_date，st_date

所有3列屬於不同的表：

doc 
doc_date  count(x) 
01-02-2012  2 
02-02-2012  3 

chem 
chem_date  count(x) 
04-02-2012  1 
06-02-2012  0 

stock 
st_date  count(x) 
01-02-2012  1 
03-02-2012  5 

我想寫這樣

case doc_date 
    when '01' then count(x), 
    case chem_date 
    when '01' then count(x), 
    case st_date 
    when '01' then count(x) 
    end as '01', 
case doc_date 
    when '02' then count(x), 
    case chem_date 
    when '02' then count(x), 
    case st_date 
    when '02' then count(x) 
    end as '02', 

....up to 31 days 

SELECT子句

如果某些病例陳述在同一日期有條目，例如doc_date和st_date都存在於'01-02-20 12' 然後它們各自的計數應該被添加到最終count(x)裝置count(x) + count(x)

所以，答案應該是：

01 02 03 04 05 06 07 08 09 10 11 12.. up to 31 days 
3 3 5 1  0       count(x) value for particular date 

輸出的說明：在此，日期01起始值爲2爲doc表和stock表的值爲1.因此，最終值將成爲它們的加法數3

相同的規則將適用於其他人。

任何建議如何在SQL中實現此輸出？或者其他方式？

Answer 1

這裏是展示它是如何做一個僞代碼：

select 

case when date_format(doc_date,"%d") = '01' then sum_x else null end as '01', 
case when date_format(doc_date,"%d") = '02' then sum_x else null end as '02', 
--and etc 

from (

    select doc_date, sum(doc_x) as sum_x    --sum the x value 
    from 
    (

     select doc_date,doc_x       --combine all 3 table stuff 
     from doc a 

     union all 

     select chem_date,chem_x 
     from chem a 

     union all 

     select st_date,st_x 
     from st a 
    ) h 
    group by doc_date    --use first col name as the union's col name 

) g 
limit 1,1  

如果doc，chem和st使用joins相結合，並有不同的模式，你可能需要做支點，或者使用多個連接到本身或使用case... when...：

select 

case when date_format(doc_date,"%d") = '01' then sum_x else null end as '01', 
case when date_format(doc_date,"%d") = '02' then sum_x else null end as '02', 
--and etc 

from (

     select doc_date,        
       a_x + b_x + c_x as sum_x   --sum them according to date 
     from (select ... from doc where ...) a 
     left join (select ... from chem where ...) b on a.doc_date=b.doc_date and --some join condition 
     left join (select ... from st where ...) c on a.doc_date=c.doc_date and --some join condition 

) g 
limit 1,1  

我與這裏的曖昧問題的工作，所以需要澄清，