连接两个表，其中table1.id等于table2.table1_id，但仅显示table1.id中在table2.table1_id中找不到的行

Question

I'm building a form for an award where the nominees can choose multiple award categories to apply to, and answer a series of questions for each award they have chosen.

I have 2 tables.

The first table contains the award categories of the award:

id: 1, 2, 3, ...

name: award1, award2, award3, ....

The second table contains the answers with the nominee id, question id, and award category:

id:

answer_id: 1, 2, 3, ...

nominee_id: 1, 1, 2, ...

question_id: 1,2, 1, ...

category_id: 1, 3, 1, ...

answer: answer 1, answer 2, answer 3, ...

What I need is a query that can display the award categories that the nominee has already submitted answers for, as well as a second query that can display the award categories that are still available for the nominee to apply to.

So using the example above, I would like to see:

1. nominee_id 1 has already applied to award1 and award 3
2. nominee_id 1 can still apply for award 2, award 4, ...

EDIT:

Here are the tables, first one is the award categories, second one is the answers

As you can see, nominee with ID of 28 has answered a total of 16 questions, 8 per award category with id of 5 and 6.

The outputs I want are:

a) display the names of the categories nominee 28 has entered in. In this case, Brand Engagement (id:5) and Corporate Social Enterprise (id:6)

b) render a dropdown menu consisting of only the categories nominee 28 has yet to enter. In this case, award category id of 7-8.

Answer 1

Try Queries as below

Query-1

nominee_id 1 has already applied to award1 and award 3

select table1.*,table2.nominee_id,table2.answer_id,table2.question_id,
table2.category_id,table2.answer from table1 
inner join table2 on table1.id = table2.category_id 

Query-2

nominee_id 1 can still apply for award 2, award 4, ...

select table1.*,table2.nominee_id,table2.answer_id,table2.question_id,
table2.category_id,table2.answer from table1 
inner join table2 on table1.id <> table2.category_id 

I have assumed fields, please ignore fields not required.

Answer 2

Building on Sameer's answer i would suggest:

First Query (Categories with participation; effectively the same as Sameer's)

SELECT table1.*, table2.nominee_id, table2.answer_id, table2.question_id, table2.category_id, table2.answer
FROM table1 
JOIN table2 ON table2.category_id = table1.id

Second Query (Categories with no participation; less "noise")

SELECT table1.*
FROM table1 
LEFT JOIN table2 ON table2.category_id = table1.id
WHERE table2.category_id IS NULL

The second query uses the way a LEFT JOIN works: if no matching row is found in table2 all columns are set to NULL inside the result. As the join criteria says table2.category_id = table1.id table2.category_id can only be NULL if table1.id is NULL or there is no row.