CREATE TABLE table_19453 ("Virtual" FLOAT, "Physical" FLOAT, "Call sign" CLOB, "Branding" CLOB, "Network" CLOB, "Owner" CLOB)

Name the number of virtual for NBC
SELECT COUNT("Virtual") FROM table_19453 WHERE "Network" = 'NBC'
SELECT COUNT("Virtual") FROM "table_19453" WHERE "Network" = 'NBC'