user: Question: Which league's playoffs was National Semi-Finals?
Columns: ['Year', 'Division', 'League', 'Regular Season', 'Playoffs', 'Open Canada Cup']
Types: ['real', 'real', 'text', 'text', 'text', 'text']
Sample row: [2000.0, 4.0, 'USL PDL', '6th, Heartland', 'Did not qualify', 'Did not participate']
SQL:

assistant: SELECT "League" FROM "Table" WHERE "Playoffs" = 'National Semi-Finals';