使用JOIN过滤数据

Question

I have this data in a table called PROD

| Project | Position | Status |
|---------|----------|--------|
| 1       | 1        | A      |
| 1       | 2        | A      |
| 2       | 1        | A      |
| 2       | 2        | B      |
| 3       | 1        | B      |
| 3       | 2        | B      |
| 4       | 1        | A      |
| 4       | 2        | A      |

I'm trying to get all the Projects that has at least one Position with Status = B .

| Project | Position | Status |
|---------|----------|--------|
| 2       | 1        | A      |
| 2       | 2        | B      |
| 3       | 1        | B      |
| 3       | 2        | B      |

I've tried using a JOIN like this:

SELECT * FROM PROD A JOIN PROD B ON A.PROD-Project = B.PROD-Project WHERE B.PROD-Status = 'B'

This give me an empty response.

Answer 1

With EXISTS :

SELECT p.* FROM PROD p 
WHERE EXISTS (
  SELECT 1 FROM PROD
  WHERE Project = p.Project AND Status = 'B'
)

or with IN :

SELECT * FROM PROD
WHERE Project IN (SELECT Project FROM PROD WHERE Status = 'B')

If you want a solution with JOIN :

SELECT DISTINCT p.* 
FROM PROD p JOIN PROD pp
ON pp.Project = p.Project 
WHERE pp.Status = 'B'

See the demo .
Results:

> Project | Position | Status
> ------: | -------: | :-----
>       2 |        1 | A     
>       2 |        2 | B     
>       3 |        1 | B     
>       3 |        2 | B 

Answer 2

You could try using a join wit the subquery

select * from  PROD 
INNER JOIN (
  select  distinct project 
  from  PROD 
  where status ='B';
  ) t on t.project = PROD.project 

Answer 3

I'm trying to get all the Projects that has at least one Position with Status = B.

No need for a JOIN, just do:

SELECT DISTINCT PROD.Project WHERE PROD.Status='B'