Question

Sorry for the confusing question, I will try to clarify.

I have an SQL database ( that I did not create ) that I would like to write a query for. I know very little about SQL, so it is hard for me to even know what to search for to see if this question has already been asked, so sorry if it has. It should be an easy solution for those in the know.

The query I need is for a search I would like to perform on an existing data management system. I want to return all the documents that a given user has NOT signed-off on, as indicated by rows in a signoffs_table. The data is stored similarly to as follows: (this is actually a simplification of the actual schema and hides several LEFT JOINS and columns)

signoffs_table:
| id | user_id | document_id | signers_list |

The naive solution I had was to do something like the following:

SELECT document_id from signoffs_table WHERE (user_id <> $BobsID) AND signers_list LIKE "%Bob%";

This works if ONLY Bob signs the document. The problem is that if Bob and Mary have signed the document then the table looks like this:

signoffs_table:
-----------------------------------------------
| id | user_id | document_id | signers_list   |
-----------------------------------------------
| 1  | 10      | 100         | "Bob,Mary,Jim" |
| 2  | 20      | 100         | "Bob,Mary,Jim" |
-----------------------------------------------

(assume Bob's ID = 10 and mary's ID = 20). 

and then when I do the query then I get back document_id 100 (in row #2) because there is a row that Bob should have signed, but did not.

Is what I am trying to do possible with the given database structure? I can provide more details if needed. I am not sure how much details are needed.

Answer 1

I guess this query is what you mean:

SELECT document_id FROM signoffs_table AS t1
WHERE signers_list LIKE "%Bob%"
AND NOT EXISTS (
    SELECT 1 FROM signoffs_table AS t2
    WHERE (t2.user_id = $BobsID) AND t2.document_id = t1.document_id )