Database schema:

CREATE TABLE "Answer" (
	"AnswerText" TEXT -- example: ['44', '37'],
	"SurveyID" INTEGER -- example: ['2014', '2016'],
	"UserID" INTEGER -- example: ['2', '1'],
	"QuestionID" INTEGER -- example: ['2', '1'],
	PRIMARY KEY ("UserID", "QuestionID"), 
	CONSTRAINT fk_answer_question FOREIGN KEY("QuestionID") REFERENCES "Question" (questionid),
	CONSTRAINT fk_answer_survey FOREIGN KEY("SurveyID") REFERENCES "Survey" ("SurveyID")
)


CREATE TABLE "Question" (
	questiontext TEXT -- example: ['What is your age?', 'What is your gender?'],
	questionid INTEGER -- example: ['2', '1'],
	PRIMARY KEY (questionid)
)


CREATE TABLE "Survey" (
	"SurveyID" INTEGER -- example: ['2014', '2016'],
	"Description" TEXT -- example: ['mental health survey for 2014', 'mental health survey for 2016'],
	PRIMARY KEY ("SurveyID")
)

Question: What are the ages of the oldest and youngest user that were surveyed? Indicate their user id.
Evidence: Oldest user refer to MAX(AnswerText) where questionid = 1; Youngest user refer to MIN(AnswerText) where questionid = 1


SQL:
SELECT MAX(T1.AnswerText), MIN(T1.AnswerText) , ( SELECT T1.UserID FROM Answer AS T1 INNER JOIN Question AS T2 ON T1.QuestionID = T2.questionid WHERE T2.questionid = 1 ORDER BY T1.AnswerText LIMIT 1 ) AS "youngest id" FROM Answer AS T1 INNER JOIN Question AS T2 ON T1.QuestionID = T2.questionid WHERE T2.questionid = 1