SQL query conditioned by another table [closed] - sql

Question

Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 5 years ago.
Improve this question
Beginner with SQL in need of help here is the problem. Can be SQL stmt for any DB i am testing on postgresql.
I have the following issue for 2 SQL tables:
Table number 1
.....................
|Boy Name| Girl Name |
|--------------------|
|Michael | Anne |
|Michael | Misty |
|Michael | Simone |
|Michael | Diane |
|Michael | Ariel |
|Jack | Misty |
|Jack | Simone |
|Jack | Anne |
|Sam | Simone |
|Sam | Misty |
|Sam | Anne |
|Sam | Mini |
|Sam | Valery |
----------------------
Table number 2
..................................
|Boy Name | Anne | Misty | Simone|
|--------------------------------|
|Michael | yes | no | no |
|Jack | yes | yes | yes |
|Sam | no | no | yes |
..................................
(IDK is like a question: does a girl like a specific boy. Can be yes, no or nothing).
Desired result
A table where the query returns 2 columns:
- a row for every "no" a boy gets from a girl via table number 2.
.....................
|Boy Name| Girl Name |
|--------------------|
|Michael | Misty |
|Michael | Simone |
|Sam | Misty |
|Sam | Anne |
----------------------
You can think of the result as a new row a with a column for the boy's name and another one with the name of the girl that had "no" in table number 2 .

Answer 1

First of all, I would suggest different table design:
CREATE TABLE person
(
id INT PRIMARY KEY,
person_name VARCHAR(200),
sex CHAR(1)
);
-- possible record: 1, 'John', 'M'; 2, 'Mary', 'F';
CREATE TABLE person_symphaty
(
person_id INT, -- FK to person table
symphaty_person_id INT -- FK to person table
);
-- you will store here if the person likes another one. 1 point here is that you can store that person doesn't like somebody, then you need some flag, for example is_symphaty INT (then 1 will mean likes, 0 will mean dislike)
then the query itself
SELECT pm.name AS male_name, pf.name AS female_name
FROM person pm
CROSS JOIN person pf
WHERE pm.sex = 'M' AND pf.sex = 'F'
NOT EXISTS (
SELECT * FROM person_symphaty ps WHERE ps.person_id = pm.id AND ps.symphaty_person_id = pf.id
)
There could be mistakes as I didn't test these queries at all.