Question

我有一个实体类

public class TeklaEventE {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    private Integer projectId;
    private Integer drawingId;
    private Integer userId;
    private String eventType;
    private LocalDateTime eventDate; 
    private LocalDateTime modifiedDate; 
    private String projectName;
    private String userName;
    private transient int noOfUser;    
    // getter setter
}

我想通过对* , COUNT(DISTINCT userId)进行排序来对projectId进行分组来获得eventDate

我尝试了以下查询

SELECT *,COUNT(DISTINCT userId) as noOfUser FROM teklaevent group by projectId order by eventDate desc; 它给出正确的计数，但是它首先运行group by，然后运行order by，但是我需要具有不同的projectId的最新行。然后我尝试按照建议的第二个查询
select * FROM TeklaEvent where id in (select max(id) FROM TeklaEvent group by projectId) order by eventDate desc;可以完美地显示我需要的行，因为eventDate始终是当前日期。但是，当我尝试从下面的查询中获取COUNT(DISTINCT userId)时。
select *,COUNT(DISTINCT userId) as noOfUser FROM TeklaEvent where id in (select max(id) FROM TeklaEvent group by projectId) order by eventDate desc;无法给我正确的结果。

如何在单个查询中执行此操作？

Answer 1

您可以在子选择上使用联接作为计数

Products

Answer 2

这对我有用：

select a.*, t.noOfUser
from teklaevent a
inner join (
  select max(id) maxid, count(distinct userId) noOfUser
  from  teklaevent
  group by projectId
) t on a.id = t.maxid;

MYSQL单一查询，用于获得COUNT（DISTINCT columnName）以及group by和order by

2 个答案: