Question

I’m totally new to SQL so I guess my question is quite simple but I wasn’t able so far to peform the desired output by myself.

I did a survey and asked 3 people to solve assignment A (with 3 tasks) and 3 people to solve assignment B (with 3 tasks).

And then I made a table which looks like this:

Table: Results
+---------+---------+---------+---------+---------+
| ID      | AssgnID | Answer1 | Answer2 | Answer3 |
+---------+---------+---------+---------+---------+
| 1       | A1      | 20      | 45      | 80      |   
| 2       | A1      | 22      | 40      | 82      |  
| 3       | A1      | 25      | 39      | 85      |
| 4       | A2      | 45      | 10      | 75      |
| 5       | A2      | 50      | 15      | 72      |
| 6       | A2      | 50      | 12      | 80      |
+---------+---------+---------+---------+---------+

What I now want to do is, to show for AssgnID A1 and A2 all the Answers in one row like this:

Table: Results per AssgnID
+---------+---------+---------+---------+---------+--------+---------+---------+--------+---------+---------+
| ID      | AssgnID | Answer1 | Answer2 | Answer3 |Answer4 | Answer5 | Answer6 |Answer7 | Answer8 | Answer9 |
+---------+---------+---------+---------+---------+---------+---------+---------+-------+---------+---------+
| 1       | A1      | 20      | 45      | 80      | 22     | 40      | 82      | 22     | 40      | 82          
| 2       | A2      | 45      | 10      | 75      | 50     | 15      | 72      | 50     | 12      | 80                  
+---------+---------+---------+---------+---------+---------+---------+---------+-------+---------+---------+

I’m able to show the distinct AssgnID by using DISTINCT or GROUP BY but I can’t show all the results in the same output.

Do I have to try something with a JOIN?

I appreciate your help a lot. thanks

Answer 1

If you are willing to accept your list of answers as a comma-separated list rather than actual columns, you can use PostgreSQL’s string_agg() to force them into a list by concatenating the three answer columns from each row into a unit, then grouping all of those together:

SELECT 
  AssgnID,
  /* Concat the 3 answers together with `,`, the group all rows together separated by `,` */
  string_agg((Answer1 || ',' || Answer2 || ',' || Answer3), ',') AS Answers
FROM yourtable
GROUP BY AssgnID

Would produce:

A1   20,45,80,22,40,82,22,42,82
A2   45,10,75,50,15,72,50,12,80

If you need to perform additional SQL operations, however, the best course of action and best permanent solution is to redesign your table structure to store these answers in a normalized way. This method defines the survey in one table, and another table holds one row per answer, or three rows per SurveyID.

Table Surveys

SurveyID
AssgnID
UserID

Table Answers

SurveyID
Answer
Value