mysql - 计算多个表给我相同的结果

Question

我有两张桌子，想计算两张桌子上的身份证号码。一张表只会有一个结果，但另一张可能会有更多。

select 
a.ID,
count(a.ID),
count(b.ID)
from a

join b on
(b.ID=a.ID)

where a.ID='7820193'
group by a.ID

结果看起来像这个 ID 7820193 count (a.ID)=200 count(b.ID)=200

但是，在我尝试过的所有类型的连接（左、右、内）中，只有一个该 ID 号的实例我做错了什么？

Answer 1

这应该可以解决问题：

SELECT
  Derived.id,
  COUNT(*),
  Derived.count

FROM(
  SELECT
    id,
    COUNT(*) AS count

  FROM a

  WHERE id = 7820193
) AS Derived

JOIN b AS b ON b.id = Derived.id

Answer 2

select 
    a.id, 
    count(a.id),
    b.id,
    count(b.id)
from a,b 
where a.id = b.id and a.id = ''7820193'
group by 
    a.id,
    b.id;

Answer 3

试试看。

SELECT a.ID, COUNT(a.ID) counta, (SELECT COUNT(b.ID) FROM b WHERE b.ID = a.ID  GROUP BY b.ID) AS countb
FROM a 
WHERE a.ID='7820193' GROUP BY a.ID

Answer 4

这应该会给你预期的结果，试一试:)

SELECT 
    z.id,
    count(a.id) as count_ID_from_Table_A,
    count(b.id) as count_ID_from_Table_B
FROM
   (SELECT ID FROM table1
    UNION
    SELECT ID FROM table2) z
LEFT JOIN 
    table1 a ON z.id=a.id
LEFT JOIN 
    table2 b ON z.id=b.id
GROUP BY 
    z.id