user: Question: How many times does the call sign XEZV appear?
Columns: ['Call sign', 'Launched', 'Transmitting from', 'Coverage', 'Languages', 'Frequency']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['XEZV', '10 May 1979', 'Guerrero ( Tlapa de Comonfort )', 'Guerrero Oaxaca Puebla', 'Nahuatl Mixtec Tlapanec', '800 AM']
SQL:

assistant: SELECT COUNT("Transmitting from") FROM "Table" WHERE "Call sign" = 'XEZV';