如何計算（SQL）中的行數？

Question

我有兩個表 A、B，我的查詢顯示它：（加入 A 和 B）

select A.i,A.j,B.x,B.y,B.z from A inner join B on A.id=B.id_B order by A.i,A.j

.

+-----+-----+-----+-----+-----+
| A.i | A.j | B.x | B.y | B.z |
+=====+=====+=====+=====+=====+
|  bk | bg  |  1  | inf1| bar | 
+-----+-----+-----+-----+-----+
|  bk | bg  |  2  | inf2| bar | 
+-----+-----+-----+-----+-----+
|  bk | bg  |  3  | inf3|  y  | 
+-----+-----+-----+-----+-----+
|  ro | fn  |  5  | enf1| bar | 
+-----+-----+-----+-----+-----+
|  ro | fn  |  3  | enf2| bar | 
+-----+-----+-----+-----+-----+
|  st | st  |  3  | onf1| bar | 
+-----+-----+-----+-----+-----+

現在我想知道是多少次

艾

重復，像這樣：

    +-----+-----+-----+-----+-----+
    | A.i | A.j | B.x | B.y | B.z |RepeatColumn
    +=====+=====+=====+=====+=====+---
    |  bk | bg  |  1  | inf1| bar | 3 |(bk is repeated 3 times)
    +-----+-----+-----+-----+-----+---
    |  bk | bg  |  2  | inf2| bar | 3 |(bk is repeated 3 times)
    +-----+-----+-----+-----+-----+---
    |  bk | bg  |  3  | inf3|  y  | 3 |(bk is repeated 3 times)
    +-----+-----+-----+-----+-----+---
    |  ro | fn  |  5  | enf1| bar | 2 |(ro is repeated 2 times)
    +-----+-----+-----+-----+-----+---
    |  ro | fn  |  3  | enf2| bar | 2 |(ro is repeated 2 times)
    +-----+-----+-----+-----+-----+---
    |  st | st  |  3  | onf1| bar | 1 |(st is repeated once)
    +-----+-----+-----+-----+-----+---

我怎么能做這個查詢，有人知道嗎？

Answer 1

你需要subquery ：

select A.i,A.j,
       B.x,B.y,B.z,
       (select count(*) from b where b.id = a.id) RepeatColumn
from A 
inner join B 
order by A.i,A.j;

但是，我沒有在 o/p 中找到表（ A ， B ）之間的任何關系。 所以，我只是在飛行中使用。

Answer 2

編輯：不幸的是（對你來說）它看起來 MySQL 不支持簡單的窗口函數。

像這樣：

COUNT(1) OVER
  ( PARTITION BY A.i
  ) AS cnt

這取決於您的用例是否比您所展示的更復雜，是否值得拼湊 group_concat 解決方法，或者只是使用子查詢來獲取計數。

Answer 3

從表名中選擇計數（AI）；

Answer 4

 select A.i,
 A.j, 
 B.x, 
 B.y,
 B.z, 
 count(A.i) as repeated_column 
 from A inner join B
 order by A.i, A.j

Answer 5

嘗試使用subquery

SELECT 
A.i,
A.j,
B.x,
B.y,
B.z,
(SELECT COUNT(1) FROM A as WHERE i = A.i) AS 'RepeatColumn'
FROM A 
INNER JOIN B 
ORDER BY A.i,A.j