Update all fields in a column from subquery postgresql - postgresql

Question

I have one table, say buchas containing a list of products. I had to create another table buchas_type with the type (class if you will) of the products in buchas.
Now I have to reference the class of product in buchas, by adding a type_id column.
So, my problem can be divided in two parts:
I need a subquery to "guess" the product type by its name. That should be somewhat easy, since the name of the product contains somewhere the name of its type. Example:
-----------------Name----------------- | ---Type---
BUCHA GOB 1600 GOB
The problem is I have a type GOB(2) that will mess things up with the type GOB. (I have also other look alike types raising the same problem).
So far, I got this:
SELECT buchas_type.id
FROM buchas_type
JOIN buchas ON buchas.description LIKE '%' || buchas_type.type || '%'
ORDER BY length(type) desc LIMIT 1;
That will solve the problem with the look alike types, since it returns the longest match. However, I need a WHERE clause otherwise I get always the same buchas_type_id. If I try for instance Where buchas.id = 50 I get a correct result.
The second part of the problem is the UPDATE command itself. I need to fill up the recently created buchas_type_id from the subquery I showed in (1). So, for every row in buchas, it has to search for the type in buchas_type using the current row's description as a parameter.
How to achieve that?

Answer 1

Assuming you have a primary key on buchas, the first part of your problem can be solved with distinct on.
select * from buchas;
buchas_id | description | buchas_type_id
-----------+-------------------+----------------
1 | BUCHA GOB 1600 |
2 | BUCHA GOB(2) 1700 |
(2 rows)
select * from buchas_type;
buchas_type_id | type
----------------+--------
1 | GOB
2 | GOB(2)
(2 rows)
select distinct on (b.buchas_id) b.buchas_id, t.buchas_type_id, b.description, t.type
from buchas b
join buchas_type t
on b.description ilike '%'||t.type||'%'
order by b.buchas_id, length(t.type) desc;
buchas_id | buchas_type_id | description | type
-----------+----------------+-------------------+--------
1 | 1 | BUCHA GOB 1600 | GOB
2 | 2 | BUCHA GOB(2) 1700 | GOB(2)
(2 rows)
With this solved, you can do an update...from:
with type_map as (
select distinct on (b.buchas_id) b.buchas_id, t.buchas_type_id
from buchas b
join buchas_type t
on b.description ilike '%'||t.type||'%'
order by b.buchas_id, length(t.type) desc
)
update buchas
set buchas_type_id = t.buchas_type_id
from type_map t
where t.buchas_id = buchas.buchas_id;
UPDATE 2
select * from buchas b join buchas_type t on t.buchas_type_id = b.buchas_type_id;
buchas_id | description | buchas_type_id | buchas_type_id | type
-----------+-------------------+----------------+----------------+--------
1 | BUCHA GOB 1600 | 1 | 1 | GOB
2 | BUCHA GOB(2) 1700 | 2 | 2 | GOB(2)
(2 rows)