在 PostgreSQL 中连接表

Question

我无法使用 PostgreSQL 从多个表中将数据放入一个表中。我有以下两个表：

schedule.event：

 | starttime  | endtime    | hash |
 | 1612716238 | 1612716266 | xyz  |
 | 1612716912 | 1612718972 | abc  |

schedule.resource：

 | name     | type      | hash |
 | sat1     | satellite | xyz  |
 | station1 | station   | xyz  |
 | modem1   | modem     | xyz  |
 | sat2     | satellite | abc  |
 | station1 | station   | abc  |
 | modem1   | modem     | abc  | 

我想获取如下表格格式的数据：

 | starttime  | endtime    | satellite | station  | modem  |
 | 1612716238 | 1612716266 | sat1      | station1 | modem1 |
 | 1612716912 | 1612718972 | sat2      | station1 | modem1 |
 

我在编写 PostgreSql 查询来执行此操作时遇到问题。

谢谢

Answer 1

你需要条件聚合如下：

Select t1.starttime, t1.endtime, t1.hash,
       Max(case when t2.type = 'satelite' then name end) as satelite,
       Max(case when t2.type = 'station' then name end) as station,
       Max(case when t2.type = 'modem' then name end) as modem
  From event t1
  Join resource t2 on t1.hash = t2.hash
  Group by t1.starttime, t1.endtime, t1.hash;