user: Question: When the call sign is WPIB, what is lowest ERP W?
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'real', 'text', 'real', 'text', 'text']
Sample row: ['WJYA', 89.3, 'Emporia, Virginia', 2000.0, 'A', 'FCC']
SQL:

assistant: SELECT MIN("ERP W") FROM "Table" WHERE "Call sign" = 'WPIB';