MySQL的 - 跨表計數

Question

我試圖執行跨多個，鏈接表計數：

select 
    vpp.Name 
    ,count(sx.Occurences) as sx_Occurences 
    ,count(vpp.Occurences) as vpp_Occurences 
    ,count(sd.Occurences) as sd_Occurences 
from v_p vpp 
    left outer join s_x sx on sx.ID = vpp.ID 
    left outer join s_d sd on sd.ID = vpp.ID 
    group by vpp.Name 

但是這給了我不正確的結果（在一個表上做一個只計數正常，但只要我添加第二個（或第三，第四......）的數字是錯誤的

Answer 1

我相信你正在尋找這樣的：的至少2 n之間的關係：

SELECT vpp.Name, 
     (SELECT count(sx.Occurences) FROM s_x WHERE s_x.ID = vpp.ID) as sx_Occurences, 
     count(vpp.Occurences) as vpp_Occurences, 
     (SELECT count(sd.Occurences) FROM s_d WHERE s_d.ID = vpp.ID) as sd_Occurences 
    FROM v_p vpp 
GROUP BY vpp.Name; 

Answer 2

你可能有1 3張桌子他的結果是你將有更多的記錄，如果你按照每張表格單獨記錄記錄的話，你會得到更多的記錄。

如果要算定域的不同值，然後使用計數（不同的...）：

select 
    vpp.Name 
    ,count(distinct sx.Occurences) as sx_Occurences 
    ,count(distinct vpp.Occurences) as vpp_Occurences 
    ,count(distinct sd.Occurences) as sd_Occurences 
from v_p vpp 
    left outer join s_x sx on sx.ID = vpp.ID 
    left outer join s_d sd on sd.ID = vpp.ID 
    group by vpp.Name 

否則，你需要做的每個表單獨計數。您可以將3個查詢合併爲子查詢：

select 
    t1.Name 
    ,sx_Occurences 
    ,vpp_Occurences 
    ,sd_Occurences 
from 
    (select name, id, count(vpp.Occurences) as vpp_Occurences 
    from v_p vpp 
    group by name, id) t1 
    left outer join 
    (select id, count(sx.Occurences) as sx_Occurences 
    from s_x sx 
    group by id) t2 on t1.ID = t2.ID 
    left outer join 
    (select id, count(sd.Occurences) as sd_Occurences 
    from s_d sd 
    group by id) t3 on t1.ID = t3.ID