Question: What is the category for trains numbered 16609/16610?
SQL: SELECT "Category" FROM "1-21716139-1" WHERE "Train No." = '16609/16610';

Question: What trains have a category of Express and a Weekly frequency?
SQL: SELECT "Train Name" FROM "1-21716139-1" WHERE "Category" = 'Express' AND "Frequency" = 'Weekly';

Question: What is the train name that has a destination of Tuticorin?
SQL: SELECT "Train Name" FROM "1-21716139-1" WHERE "Destination" = 'Tuticorin';

Question: What is the frequency of trains numbered 12671/12672?
SQL: SELECT "Frequency" FROM "1-21716139-1" WHERE "Train No." = '12671/12672';

Question: How many destinations have a Weekly frequency and are named AC Express?
SQL: SELECT COUNT("Destination") FROM "1-21716139-1" WHERE "Frequency" = 'Weekly' AND "Train Name" = 'AC Express';

Question: What is the number of frequencies that have a destination of Jaipur?
SQL: SELECT COUNT("Frequency") FROM "1-21716139-1" WHERE "Destination" = 'Jaipur';