Single query to collect data from multiple tables

Question

I have a problem collecting data from an SQL database that I designed.

This is a table of questions of different types, each type has it's own table with different columns and has the questionid as a foreign key that referenced this table as seen below.

 Column   |          Type          | Modifiers
------------+------------------------+-----------
 questionid | integer                | not null
 header     | character varying(500) |
Indexes:
    "quizquestion_pkey" PRIMARY KEY, btree (questionid)
Referenced by:
    TABLE "matchingpairs" CONSTRAINT "matchingpairs_questionid_fkey" FOREIGN KEY (questionid) REFERENCES quizquestion(questionid)
    TABLE "mcqchoices" CONSTRAINT "mcqchoices_questionid_fkey" FOREIGN KEY (questionid) REFERENCES quizquestion(questionid)
    TABLE "questionsinquiz" CONSTRAINT "questionsinquiz_questionid_fkey" FOREIGN KEY (questionid) REFERENCES quizquestion(questionid)
    TABLE "truefalsequestion" CONSTRAINT "truefalsequestion_questionid_fkey" FOREIGN KEY (questionid) REFERENCES quizquestion(questionid
)

I have another table that keeps up which question belongs to which quiz using also the questionid

   Column   |  Type   | Modifiers
------------+---------+-----------
 quizid     | integer | not null
 questionid | integer | not null
 index      | integer |
Indexes:
    "questionsinquiz_pkey" PRIMARY KEY, btree (quizid, questionid)
Foreign-key constraints:
    "questionsinquiz_questionid_fkey" FOREIGN KEY (questionid) REFERENCES quizquestion(questionid)
    "questionsinquiz_quizid_fkey" FOREIGN KEY (quizid) REFERENCES quiz(quizid)

Is there a way to collect all the different questions in one query or do I have to query on every question type, or is there something different that I can change in the database table design.

Answer 1

Based on your description, you can use Postgres inheritance. This is a facility where tables can be related to each other. The place to start learning about it is in the documentation .

Using inheritance, you would have a parent table called questions which defines questionId and other related columns. Then you can define multiple other tables such as matchingPairsQuestions which inherit from questions . Queries and foreign keys can then refer either to the individual "children" tables or to all of them as a single set.