Conditionally select value from one of two tables - sql

Question

I have a questionnaire application, where a user will submit answers. Some of the questions are text based and some have fixed options.
The values are saved to the tAnswers table as either the entered text value, or the Id of the selected option. There is a QuestionTypeId column which defines if the answer is a reference to tOptions.Id.
I want to select the answers, returning the entered value or the value related to the selected Id.
For example;
SET NOCOUNT ON
DECLARE #tSubmissions TABLE (Id INT)
DECLARE #tSubmissionQuestions TABLE (SubmissionId INT, QuestionId INT)
DECLARE #tQuestions TABLE (Id INT, QuestionText NVARCHAR(MAX), ColName NVARCHAR(MAX), QuestionTypeId INT)
DECLARE #tOptions TABLE (Id INT, OptionValue NVARCHAR(MAX), OptionGroupId INT)
DECLARE #tAnswers TABLE (Id INT IDENTITY(1,1), SubmissionId INT, QuestionId INT, AnswerValue NVARCHAR(MAX))
INSERT INTO #tQuestions VALUES (1, 'What is your name?', 'Name', 1)
INSERT INTO #tQuestions VALUES (2, 'What is your age?', 'Age', 1)
INSERT INTO #tQuestions VALUES (3, 'What is your gender?', 'Gender', 2)
INSERT INTO #tQuestions VALUES (4, 'What is your favourite colour?', 'Colour', 2)
-- Answers for question 3 - gender
INSERT INTO #tOptions VALUES (1, 'Male', 1)
INSERT INTO #tOptions VALUES (2, 'Female', 1)
-- answers for question 4 - colour
INSERT INTO #tOptions VALUES (3, 'Blue', 2)
INSERT INTO #tOptions VALUES (4, 'Green', 2)
INSERT INTO #tOptions VALUES (5, 'Red', 2)
INSERT INTO #tOptions VALUES (6, 'Yellow', 2)
INSERT INTO #tSubmissions VALUES (1)
INSERT INTO #tSubmissions VALUES (2)
INSERT INTO #tSubmissions VALUES (3)
INSERT INTO #tSubmissionQuestions VALUES (1, 1)
INSERT INTO #tSubmissionQuestions VALUES (1, 2)
INSERT INTO #tSubmissionQuestions VALUES (1, 3)
INSERT INTO #tSubmissionQuestions VALUES (1, 4)
INSERT INTO #tSubmissionQuestions VALUES (2, 1)
INSERT INTO #tSubmissionQuestions VALUES (2, 2)
INSERT INTO #tSubmissionQuestions VALUES (2, 3)
INSERT INTO #tSubmissionQuestions VALUES (2, 4)
INSERT INTO #tSubmissionQuestions VALUES (3, 1)
INSERT INTO #tSubmissionQuestions VALUES (3, 2)
INSERT INTO #tSubmissionQuestions VALUES (3, 3)
INSERT INTO #tSubmissionQuestions VALUES (3, 4)
-- form submissions
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (1, 1, 'Tony Stark')
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (1, 2, '39')
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (1, 3, '1') -- reference to #tOptions
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (1, 4, '5') -- reference to #tOptions
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (2, 1, 'Pepper Potts')
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (2, 2, '38')
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (2, 3, '2') -- reference to #tOptions
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (2, 4, '6') -- reference to #tOptions
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (3, 1, 'James Rhodes')
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (3, 2, '41') -- has choosen to not answer question 3
INSERT INTO #tAnswers (SubmissionId, QuestionId, AnswerValue) VALUES (3, 4, '3') -- reference to #tOptions
SELECT
s.Id as SubmissionId, q.Id as QuestionId, a.AnswerValue
FROM
#tSubmissions s
INNER JOIN #tSubmissionQuestions sq
ON sq.SubmissionId = s.Id
INNER JOIN #tQuestions q
ON q.Id = sq.QuestionId
LEFT JOIN #tAnswers a
ON a.QuestionId = q.Id
AND a.SubmissionId = s.Id
DBFiddle
This returns;
SubmissionId | QuestionId | AnswerValue
=============|============|===============
1 | 1 | Tony Stark
1 | 2 | 39
1 | 3 | 1 <-- this is the Id of the selected option
1 | 4 | 5 <-- this is the Id of the selected option
2 | 1 | Pepper Potts
2 | 2 | 38
2 | 3 | 2 <-- this is the Id of the selected option
2 | 4 | 6 <-- this is the Id of the selected option
3 | 1 | James Rhodes
3 | 2 | 41
3 | 3 | NULL <-- the option was not selected
3 | 4 | 3 <-- this is the Id of the option
Instead I would like;
SubmissionId | QuestionId | AnswerValue
=============|============|===============
1 | 1 | Tony Stark
1 | 2 | 39
1 | 3 | Male <-- this is the value of the selected option
1 | 4 | Red <-- this is the value of the selected option
2 | 1 | Pepper Potts
2 | 2 | 38
2 | 3 | Female <-- this is the value of the selected option
2 | 4 | Yellow <-- this is the value of the selected option
3 | 1 | James Rhodes
3 | 2 | 41
3 | 3 | NULL <-- the option was not selected
3 | 4 | Blue <-- this is the value of the selected option
How do I conditionally pull values from the tOptions table?

Answer 1

I guess this is what you're looking for:
Another LEFT JOIN on tOptions to select the values, in case of QuestionTypeId = 2
I just added the ISNUMERIC to avoid conversion errors.
SELECT
s.Id as SubmissionId,
q.Id as QuestionId,
COALESCE(t.OptionValue,a.AnswerValue) AS AnswerValue
FROM
#tSubmissions s
INNER JOIN #tSubmissionQuestions sq
ON sq.SubmissionId = s.Id
INNER JOIN #tQuestions q
ON q.Id = sq.QuestionId
LEFT JOIN #tAnswers a
ON a.QuestionId = q.Id
AND a.SubmissionId = s.Id
LEFT JOIN #tOptions t
ON q.QuestionTypeId = 2
AND ISNUMERIC(a.AnswerValue) = 1
AND a.AnswerValue = t.Id

Answer 2

I would make two columns in the Answers table. One that you have AnswerValue NVARCHAR(MAX) NULL and another one AnswerOptionID int NULL. It would make joining way more efficient and it would eliminate problems when engine tries to convert text "Tony Stark" into integer.
But, given the schema as is, here is one variant.
I added LEFT JOIN to the #tOptions table. Note, that I'm converting integer IDs into text, not other way around.
SELECT
s.Id as SubmissionId, q.Id as QuestionId
-- , a.AnswerValue, Options.OptionValue
,CASE WHEN q.QuestionTypeId = 2
THEN Options.OptionValue
ELSE a.AnswerValue
END AS AnswerText
FROM
#tSubmissions s
INNER JOIN #tSubmissionQuestions sq ON sq.SubmissionId = s.Id
INNER JOIN #tQuestions q ON q.Id = sq.QuestionId
LEFT JOIN #tAnswers a
ON a.QuestionId = q.Id
AND a.SubmissionId = s.Id
LEFT JOIN #tOptions AS Options
ON q.QuestionTypeId = 2
AND a.AnswerValue = CAST(Options.Id AS NVARCHAR(MAX))
;

Answer 3

Please try this.
SELECT
s.Id as SubmissionId, q.Id as QuestionId,
CASE WHEN q.QuestionTypeId = 1 THEN
a.AnswerValue
ELSE
ISNULL((SELECT CONVERT(VARCHAR(100),OptionValue) FROM #tOptions o WHERE o.Id = a.AnswerValue),a.AnswerValue)
END AS AnswerValue
FROM
#tSubmissions s
INNER JOIN #tSubmissionQuestions sq
ON sq.SubmissionId = s.Id
INNER JOIN #tQuestions q
ON q.Id = sq.QuestionId
LEFT JOIN #tAnswers a
ON a.QuestionId = q.Id
AND a.SubmissionId = s.Id
ORDER BY s.Id ASC