Question

我有一张这样的表：

+---------+---------+
|   id1   |   id2   |
+---------+---------+
|       1 |       2 |
|       2 |       2 |
|       3 |       1 |
|       4 |       1 |
|       5 |       3 |
|       6 |       2 |
+---------+---------+

我想，对于每个id2，计算与之关联的id1的数量，包括零值。目前我有这个：

select id2, count(*) cnt 
from mytable group by id2

部分工作，除了它产生这个输出：

+---------+---------+
|   id2   |   cnt   |
+---------+---------+
|       1 |       2 |
|       2 |       3 |
|       3 |       1 |
+---------+---------+

我想获得这样的输出：

+---------+---------+
|   id2   |   cnt   |
+---------+---------+
|       1 |       2 |
|       2 |       3 |
|       3 |       1 |
|       4 |       0 |
|       5 |       0 |
|       6 |       0 |
+---------+---------+

我怎么能实现这个目标？谢谢

Answer 1

您可以使用LEFT JOIN：

来使用以下内容

SELECT id1, IFNULL(cnt, 0) AS IDs FROM table1 LEFT JOIN (
    SELECT id2, count(*) cnt FROM table1 GROUP BY id2
)x ON table1.id1 = x.id2

演示： http://sqlfiddle.com/#!9/e97c4e/2/0

Answer 2

您需要一个包含结果集中所需值的表格。然后有几种方法。。。例如，相关子查询：

var options = { path: '/api/data/v8.2/contacts?$select=address1_city,address1_line1,address1_line2,address1_line3,contactid,emailaddress1,firstname,fullname,middlename,mobilephone,statecode,suffix,telephone1,vcm_npiid,vcm_prescriberspeciality,vcm_prescriberstatus,vcm_recordtype,vcm_symphonyid&$orderby=fullname asc&$filter=statecode eq 0',
  host: 'xxxxxx.crm.dynamics.com',
  method: 'GET',
  headers:
   { Authorization: 'Bearer xxxxxxx',
     Accept: 'application/json',
     'Content-Type': 'application/json; charset=utf-8',
     Prefer: 'odata.includeannotations=OData.Community.Display.V1.FormattedValue',
     'OData-MaxVersion': '4.0',
     'OData-Version': '4.0' 
   } 
} 

var crmrequest = https.request(options, function(response) { ... }

Answer 3

你应该试图弄清楚有多少Id2与Id1匹配，你可以通过表的左连接来实现这一点。

SELECT 
  mt1.Id1, 
  COUNT(mt2.Id2) 
FROM 
  MyTable as mt1 LEFT JOIN MyTable as mt2 ON mt1.Id1 = mt2.Id2
GROUP BY
  mt1.Id1

将包含id1的所有值，并计算id2的所有匹配项。如果Id1不匹配，则计数为0。

SQL：在表中包含计数中的零

3 个答案: