Database tables map One To Many without foreign key in @JoinColumn

Possible to not have foreign key relationship in child table to its parent in the database, while in JPA it will still be able to map out fine? How will this be done?

Can I still use @JoinColumn to define the field for reference back to the parent table?

This is a one-to-many relationship. One parent record, many child records.

I only care about writes to the database tables right now.

join f1 to f2 so that each join-able f1 record only joins once to the first available match-able in f2

Hopefully someone can help me with this. Given 2 files

f1

card1,value1,f1c11,f1c12

card2,value2,f1c21,f1c22

card3,value3,f1c31,f1c32

card4,value4,f1c41,f1c42

card4,value4,f1c411,f1c412

card4,value,f1c421,f1c422

card5,vaule5,f1c51,f1c52

f2

card,value2,f2c1,f2c2

card2,value,f2c21,f2c22

card2,value2,f2c211,f2c212

card2,value2,f2c221,f2c222

card3,value3,f2c31,f2c32

card4,value4,f2c41,f2c42

card4,value4,f2c411,f2c412

card5,vaule5,f2c51,f2c52

card6,vaule6,f2c61,f2c62

card7,vaule5,f2c71,f2c72

desired:
join f1 to f2 so that each join-able f1 record only joins once to the first available match-able in f2

card2,value2,f1c21,f1c22,f2c211,f2c212

card3,value3,f1c31,f1c32,f2c31,f2c32

card4,value4,f1c41,f1c42,f2c41,f2c42

card4,value4,f1c411,f1c412,f2c41,f2c42

card5,vaule5,f1c51,f1c52,f2c51,f2c52

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Author: Henry P

How to do left join , same table with different conditions per column

Hi i need information about how to merge both sentences

Sentence 1

select idlote from polizamovtos group by idlote having sum(cargo)-sum(abono) > 0

Sentence 2

SELECT SUM(cargo) as saldo FROM polizamovtos WHERE FECHAMOVTO='2020-01-01' GROUP BY IDLOTE

sentence 1 is the main filter

Hi, I attach more information

table polizamovtos
enter image description here

Output expected

idlote cargo
1 4000
3 4000
4 5000

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Author: Sergio Rossetti

MySQL count results from JOIN with where clause

I’ve got two tables.

chats:
id, name, type, deleted_at

user_chat:
id, user_id, chat_id, deleted_at

What I’m trying to do is to select a private chat with a user ID 1, where it’s the only participant in the chat, avoiding sub-queries.

What I tried:

SELECT count(user_chat.id) as count_users, chats.*
FROM chats
    LEFT OUTER JOIN user_chat on user_chat.chat_id = chats.id
WHERE chats.type = 'private'
    AND user_chat.user_id = 1
    AND user_chat.deleted_at IS NULL
    AND chats.deleted_at IS NULL
GROUP BY chats.id
HAVING count_users = 1;

With all variants of group, having, etc. with no luck. Please, advice.

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Author: Tim Mishutin