In 2019, how many users in the United States have a family history of mental illness?
2019 refer to SurveyID; Users in the United States refers to AnswerText = 'United States' where questionid = 3; have a family history of mental illness refers to AnswerText = 'Yes' where questionid = 6
SELECT COUNT(T1.UserID) FROM Answer AS T1 INNER JOIN ( SELECT T2.questionid FROM Answer AS T1 INNER JOIN Question AS T2 ON T1.QuestionID = T2.questionid WHERE T1.SurveyID = 2019 AND T2.questionid = 6 AND T1.AnswerText LIKE 'Yes' ) AS T2 ON T1.QuestionID = T2.questionid WHERE T1.SurveyID = 2019 AND T2.questionid = 3 AND T1.AnswerText LIKE 'United States'
database name:db_id mental_health_survey
Question table Question Cols: question text dtype text, question id dtype integer, 
Survey table Survey Cols: Survey ID dtype integer, Description dtype text, 
Answer table Answer Cols: Answer Text dtype text, Survey ID dtype integer, User ID dtype integer, Question ID dtype integer, 
