Is it possible to use STRING_SPLIT in an ORDER BY clause? - sql-server

Question

I am trying to order values that are going to be inserted into another table based on their order value from a secondary table. We are migrating old data to a new table with a slightly different structure.
I thought I would be able to accomplish this by using the string_split function but I'm not very skilled with SQL and so I am running into some issues.
Here is what I have:
UPDATE lse
SET Options = a.Options
FROM
dbo.LessonStepElement as lse
CROSS JOIN
(
SELECT
tbl1.*
tbl2.Options,
tbl2.QuestionId
FROM
dbo.TrainingQuestionAnswer as tbl1
JOIN (
SELECT
string_agg((CASE
WHEN tqa.CorrectAnswer = 1 THEN REPLACE(tqa.AnswerText, tqa.AnswerText, '*' + tqa.AnswerText)
ELSE tqa.AnswerText
END),
char(10)) as Options,
tq.Id as QuestionId
FROM
dbo.TrainingQuestionAnswer as tqa
INNER JOIN
dbo.TrainingQuestion as tq
on tq.Id = tqa.TrainingQuestionId
INNER JOIN
dbo.Training as t
on t.Id = tq.TrainingId
WHERE
t.IsDeleted = 0
and tq.IsDeleted = 0
and tqa.IsDeleted = 0
GROUP BY
tq.Id,
tqa.AnswerDisplayOrder
ORDER BY
(SELECT [Value] FROM STRING_SPLIT((SELECT AnswerDisplayOrder FROM dbo.TrainingQuestion WHERE Id = tmq.Id), ','))
) as tbl2
on tbl1.TrainingQuestionId = tbl2.QuestionId
) a
WHERE
a.TrainingQuestionId = lse.TrainingQuestionId
The AnswerDisplayOrder that I am using is just a nvarchar comma separated list of the ids for the answers to the question.
Here is an example:
I have 3 rows in the TrainingQuestionAnswer table that look like the following.
ID TrainingQuestionId AnswerText
-------------------------------------------
215 100 No
218 100 Yes
220 100 I'm not sure
I have 1 row in the TrainingQuestion table that looks like the following.
ID AnswerDisplayOrder
--------------------------
100 "218,215,220"
Now what I am trying to do is when I update the row in the new table with all of the answers combined, the answers will need to be in the correct order which is dependent on the AnswerDisplayOrder in the TrainingQuestion table. So in essence, the new table would have a row that would look similar to the following.
ID Options
--------------
193 "Yes No I'm not sure"
I'm aware that the way I'm trying to do it might not be even possible at all. I am still learning and would just love some advice or guidance on how to make this work. I also know that string_split does not guarantee order. I'm open to other suggestions that do guarantee the order as well.

Answer 1

I simplified the issue in the question to the following approach, that is a possible solution to your problem. If you want to get the results from the question, you need a splitter, that returns the substrings and the positions of the substrings. STRING_SPLIT() is available from SQL Server 2016, but is not an option here, because (as is mentioned in the documentation) the output rows might be in any order and the order is not guaranteed to match the order of the substrings in the input string.
But you may try to use a JSON based approach, with a small string manipulation, that transforms answers IDs into a valid JSON array (218,215,220 into [218,215,220]). After that you can easily parse this JSON array with OPENJSON() and default schema. The result is a table, with columns key, value and type and the key column (again from the documentation) holds the index of the element in the specified array.
Tables:
CREATE TABLE TrainingQuestionId (
ID int,
TrainingQuestionId int,
AnswerText varchar(1000)
)
INSERT INTO TrainingQuestionId
(ID, TrainingQuestionId, AnswerText)
VALUES
(215, 100, 'No'),
(218, 100, 'Yes'),
(220, 100, 'I''m not sure')
CREATE TABLE TrainingQuestion (
ID int,
AnswerDisplayOrder varchar(1000)
)
INSERT INTO TrainingQuestion
(ID, AnswerDisplayOrder)
VALUES
(100, '218,215,220')
Statement:
SELECT tq.ID, oa.Options
FROM TrainingQuestion tq
OUTER APPLY (
SELECT STRING_AGG(tqi.AnswerText, ' ') WITHIN GROUP (ORDER BY CONVERT(int, j.[key])) AS Options
FROM OPENJSON(CONCAT('[', tq.AnswerDisplayOrder, ']')) j
LEFT JOIN TrainingQuestionId tqi ON TRY_CONVERT(int, j.[value]) = tqi.ID
) oa
Result:
ID Options
100 Yes No I'm not sure
Notes: You need SQL Server 2017+ to use STRING_AGG(). For SQL Server 2016 you need a FOR XML to aggregate strings.

Answer 2

declare #TrainingQuestionAnswer table
(
ID int,
TrainingQuestionId int,
AnswerText varchar(20)
);
insert into #TrainingQuestionAnswer(ID, TrainingQuestionId, AnswerText)
values(215, 100, 'No'), (218, 100, 'Yes'), (220, 100, 'I''m not sure');
declare #TrainingQuestiontest table
(
testid int identity,
QuestionId int,
AnswerDisplayOrder varchar(200)
);
insert into #TrainingQuestiontest(QuestionId, AnswerDisplayOrder)
values(100, '218,215,220'), (100, '220,218,215'), (100, '215,218');
select *,
(
select string_agg(pci.AnswerText, '==') WITHIN GROUP ( ORDER BY pci.pos)
from
(
select a.AnswerText,
pos = charindex(concat(',', a.ID, ','), concat(',', q.AnswerDisplayOrder,','))
from #TrainingQuestionAnswer as a
where a.TrainingQuestionId = q.QuestionId
and charindex(concat(',', a.ID, ','), concat(',', q.AnswerDisplayOrder,',')) >= 1
) as pci
) as TestAnswerText
from #TrainingQuestiontest as q;