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: How many users lived in Canada according to 2018's survey?
Evidence: lived in Canada refers to AnswerText(QuestionID(3)) = 'Canada'

SQL:
SELECT COUNT(T2.UserID) FROM Question AS T1 INNER JOIN Answer AS T2 ON T1.questionid = T2.QuestionID WHERE T2.SurveyID = 2018 AND T1.questiontext = 'What country do you live in?' AND T2.AnswerText = 'Canada'