postgres 分组

Question

I am having a db names products where i wanted to select the price of each product based on the id, but the price that i stored in the table is from different sources. So i want one latest price from each of the source. My table looks like this

id | name | source | updated_at | price 
1  | ace  | vanil  | ...        | 100
2  | vax  | vanil  | ...        | 101
3  | tax  | sunyil | ...        | 200
1  | ace  | sunyil | latest     | 99.5
2  | vax  | sunyil | latest     | 100.5
3  | tax  | vanil  | latest     | 199.5
3  | tax  | vanil  | ...        | 220
3  | tax  | vanil  | ...        | 211
3  | tax  | vanil  | ...        | 205
3  | tax  | sunyil | ...        | 211
3  | tax  | vanil  | ...        | 220
3  | tax  | sunyil |latest_time | 220
1  | ace  | sunyil | ...        | 101

i want the output to be like this when my where condition is for id=3

id | name | source | updated_at | price
 3 | tax  | vanil  | latest time| 199.5
 3 | tax  | sunyil | latest time| 220

i tried running the

select * from products WHERE id= '3' ORDER BY updated_at DESC LIMIT 1 

but this one brings only one row irrespective of the source

could any one help me out with this. I am extremely new to postgres and sql queries. I would really appreciate your help.

Answer 1

Using DISTINCT ON :

SELECT DISTINCT ON (id, source) *
FROM products
WHERE id = 3
ORDER BY id, source, updated_at DESC;

Answer 2

It's not really clear what you want to do. If you would like to sum the price for the product with id 3 not having the text "..." in the column "updated_at", you can do this query:

SELECT id, name, source, updated_at, SUM(price) FROM products 
WHERE id = 3 and updated_at != '...'
GROUP BY id, name, source, updated_at ORDER BY updated_at;

See this example and try out: db<>fiddle Modify the query to your desires if necessary.