พล็อตปีโดยค่าเฉลี่ยของการเข้างานเป็นแผนภูมิเส้นไม่จำเป็นต้องใช้ตารางทั้งหมด
Plot year by the average of attendance as a line chartIt is not neccessary to use all the tables.
 batting_postseason:  year [ INTEGER]  round [ TEXT]  player_id [ TEXT]  team_id [ TEXT]  league_id [ TEXT]  g [ INTEGER]  ab [ INTEGER]  r [ INTEGER]  h [ INTEGER]  double [ INTEGER]  triple [ INTEGER]  hr [ INTEGER]  rbi [ INTEGER]  sb [ INTEGER]  cs [ NUMERIC]  bb [ INTEGER]  so [ INTEGER]  ibb [ NUMERIC]  hbp [ NUMERIC]  sh [ NUMERIC]  sf [ NUMERIC]  g_idp [ NUMERIC] 
SELECT year, AVG(attendance) FROM home_game GROUP BY year