Monsters of Rock จะมีการแสดง 12 วงดนตรีเมื่อใด?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
When is the Monsters of Rock show with 12 bands?It is not neccessary to use all the tables.
 table_31803:  "Year" [ real]  "Date" [ text]  "Event" [ text]  "Days" [ text]  "Stages" [ text]  "Acts" [ text] 
SELECT "Date" FROM table_31803 WHERE "Event" = 'monsters of rock' AND "Acts" = '12 bands'