Question

我有下表：

URL url = Thread.currentThread().getContextClassLoader().getResource("tourneeCollecteRawOutputCalculIndicateur.json");
File file = new File(url.getPath());
InputStream in = new FileInputStream(file)
Reader r = new InputStreamReader(in, StandardCharset.ISO_8859_1);
TourneeCollecteRawOutput tourneeCollecteRawOutput = mapper.readValue(in, mapper.getTypeFactory().constructCollectionType(List.class, TourneeCollecteRawOutput.class));

我在带有表A的Enterpr_id上有一个外键，我该如何进行计数转换并获得预期的输出：

Table A:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   ID  |   User    |   Enterpr_id    |
|   1   |   test1   |      1          |
|   2   |   test2   |      2          |
|   3   |   test3   |      3          |
|   4   |   test4   |      4          |
|   5   |   test5   |      1          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Enterpr_id    |     Name    |
|   1             |   Nespresso |
|   2             |     what    |
|   3             |     else    |
|   4             |     need    |
|   5             |     help    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Answer 1

这是一个简单的连接：

select a.user, b.name
from tablea a
inner join tableb b on b.entrepr_id = a.entrepr_id

编辑：从更新后的问题中，您似乎想要汇总和一个left join：

select b.name, count(a.id) cnt_users
from tableb b
left join tablea a on a.entrepr_id = b.entrepr_id 
group by b.entrepr_id, b.name
order by b.entrepr_id

Answer 2

这是一个带有计数的左联接查询：

animalData

计算具有相同值的行数

2 个答案: