Question

我有两张桌子 - '提供'和'加入'。我需要从连接表中计算'provided_id'并在未找到时计为零。我的表格和输出要求如下。如何在mysql中使用单个查询来实现这一点？

TABLE : OFFERED
===============
offered_id    data
-----------   ----
    1         aaaa
    2         bbbb
    3         cccc
    4         dddd
    5         eeee
    6         ffff

TABLE : JOINED
===============
joined_id      offered_id
-----------    ----------
    1               5
    2               2
    3               2
    4               1
    5               3
    6               2
    7               5

OUTPUT REQUIRED
===============
offered_id      data     count(offered_id) from joined table.(0 for no entry)
-----------    -----     ------------------------------------------------
    1           aaaa          1
    2           bbbb          3
    3           cccc          1
    4           dddd          0
    5           eeee          1
    6           ffff          0

Answer 1

使用count：

SELECT OFFERED.OFFERED_id,OFFERED.data,(select count(JOINED.joined_id) FROM JOINED INNER JOIN OFFERED
ON JOINED.offered_id = OFFERED.offered_id) as count_joined FROM OFFERED

Answer 2

尝试一下，它帮助我为我的项目实现同样的目标，它一定会帮助你。

import numpy as np
import pandas as pd
df = pd.read_csv("phased.txt")
match_counts = {(i,j): 
                   np.sum(df[df.columns[i]] != df[df.columns[j]]) 
                           for i in range(3,len(df.columns))
                           for j in range(3,len(df.columns))}

match_counts
{(6, 4): 3,
 (4, 7): 2,
 (4, 4): 0,
 (4, 3): 3,
 (6, 6): 0,
 (4, 5): 3,
 (5, 4): 3,
 (3, 5): 3,
 (7, 7): 0,
 (7, 5): 3,
 (3, 7): 2,
 (6, 5): 3,
 (5, 5): 0,
 (7, 4): 2,
 (5, 3): 3,
 (6, 7): 2,
 (4, 6): 3,
 (7, 6): 2,
 (5, 7): 3,
 (6, 3): 2,
 (5, 6): 3,
 (3, 6): 2,
 (3, 3): 0,
 (7, 3): 2,
 (3, 4): 3}

Answer 3

使用子查询可以实现...

SELECT OFFERED.offered_id, OFFERED.data, (SELECT COUNT(JOINED.joined_id) FROM JOINED WHERE JOINED.offered_id = OFFERED.offered_id) AS count_joined FROM OFFERED

如何在mysql中使用单个查询从另一个表（没有数据时为零）计数？

3 个答案: