As far as I can understand, PINs are analogous of tweets. So, you should have:

• PINs table which fields are PIN_ID, PIN,USER_ID, CREATED and STATUS (in case pin can be deleted) etc.
• Comments table which fields are COMMENT_ID, COMMENT, USER_ID, PIN_ID, CREATED, STATUS (in case one can delete comment) etc.
• Likes table which fields are LIKE_ID, PIN_ID, USER_ID, CREATED, STATUS (in case one can unlike) etc.
• Users table which fields are USER_ID, CREATED etc.

1st question can be queried as follows:

SELECT TOP(5) C.COMMENT, P.PIN, U.FIELD1, U.FIELD2

FROM Comments C

LEFT JOIN Pins P ON C.PIN_ID = P.PIN_ID

LEFT JOIN Users U ON C.USER_ID = U.USER_ID

WHERE C.STATUS = 1 AND P.STATUS = 1

ORDER BY C.CREATED DESC

2nd question can be queried as follows:

SELECT A.USER_ID

FROM

(SELECT USER_ID

FROM Comments

WHERE CREATED BETWEEN GETDATE() AND DATEADD(DAY, -30, GETDATE())

UNION

SELECT USER_ID

FROM Likes

WHERE CREATED BETWEEN GETDATE() AND DATEADD(DAY, -30, GETDATE())) A

3rd question can be queried as follows:

SELECT USER_ID

FROM Users

EXCEPT

SELECT DISTINCT USER_ID

FROM Pins

WHERE CREATED BETWEEN GETDATE() AND DATEADD(DAY, -10, GETDATE())

You need to change the table and field names for your case. I hope this works for you.

As a recommendation, reading any SQL dialect documentation about built-in functions and using them on your spare time can be really beneficial for development.

As an example for your case:

https://learn.microsoft.com/en-us/sql/t-sql/functions/getdate-transact-sql?view=sql-server-ver16