SELECT * FROM questions WHERE test_id - mysql

Question

I have two SQL tables:
Tests
id | name
1 | simple
2 | advanced
3 | professional
Questions
id | Question | answer a | answer b | test_id
1 | Working? | Yes | no | 1,3
2 | Do you smoke? | Yes | no | 2,3
3 | You have a driving license? | Yes | No | 2
Questions should be displayed only if in "test_id" is the id of the desired test, for example, test 2 should contain only questions 2 and 3
SELECT * FROM questions WHERE... (array "test_id" contains 2)
It isn't duplicate, because in suggested question is query like "WHERE ... value=(1,2,3,4)", but in my problem, I have query like "... WHERE (1,2,3,4,5)=value" it's opposite and method "in" is not correct.

Answer 1

You should normalize your database, creating a third table to link questions with the tests they appear on:
Tests:
id | name
1 | simple
2 | advanced
3 | professional
Questions:
id | question | answer a | answer b
1 | Working? | Yes | No
2 | Do you smoke? | Yes | No
3 | You have a driving license? | Yes | No
TestQuestions:
id | test_id | question_number | question_id
1 | 1 | 1 | 1
2 | 2 | 1 | 2
3 | 2 | 2 | 3
4 | 3 | 1 | 1
5 | 3 | 2 | 2
You can then fetch the questions for an individual test by joining the TestQuestions table with Questions:
SELECT Questions.*
FROM TestQuestions
INNER JOIN Questions ON Questions.id = TestQuestions.question_id
WHERE TestQuestions.test_id = 2
ORDER BY TestQuestions.question_number
If you are unable to modify your database tables, then you could also determine the questions in a test using MySQL's FIND_IN_SET function:
SELECT * From Questions WHERE FIND_IN_SET('2', test_id) > 0
It is preferable to use the normalized database structure though since this allows the ordering of questions on a test to be expressed and indexes can also be created to allow better performance.
To evaluate the FIND_IN_SET query, the database must consider every row in the Questions table to see if it matches. By adding the following index to the normalized database, the database would be able to seek directly to the relevant questions for a test:
CREATE UNIQUE INDEX test_id_question_number ON TestQuestions (test_id, question_number)

Answer 2

You really should include another table that maps the question to the test. The way you have it now, the questions cannot be easily linked to the test. For example, if you try to use use a LIKE comparison you may get questios back you didn't intend. Say you are looking for questions to test 2
SELECT * FROM questions WHERE test_id LIKE %2%;
You would also retrieve items for tests 12, anything in the 20s and 32, 42, etc.
You should create a new table called testquestions (for example). This would have two fields
test_id
question_id
And then this data (using what you showed above)
test_id | question_id
1 | 1
2 | 2
2 | 3
3 | 1
3 | 2
Now you can run a query like this
SELECT
tests.name,
questions.question,
questions.`answer a`,
questions.`answer b`
FROM (
tests LEFT JOIN testquestions ON test.id=testquestion.test_id
) LEFT JOIN
questions ON questions.id = testquestion.question_id
WHERE
tests.id = 2;

Answer 3

If you need to search one test id at a time you can use
SELECT * FROM questions WHERE (',' + test_id + ',') like '%,1,%'

Answer 4

i think the best solution offer you Phil Ross (only think i would change will be that i would store this Yes/No answer as true/false OR small int and 0/1)... But if you want to keep your table like they are you can do something like this
SELECT q.* FROM Questions q
INNER JOIN tests t
ON t.id = 2
AND q.test_id regexp(CONCAT('(^|,)',t.id, '(,|$)'));
Here is SQL Fiddle to see how it's work...
P.S. The query connect and the first table so you can select value from there if it's needed...
GL!
EDIT: Fixed on Phil suggestion... Tnx Phil :)