SELECT count(*) FROM city WHERE county_ID IN (SELECT county_ID FROM county_public_safety WHERE population  >  20000)
How many cities are in counties that have populations of over 20000?
CREATE TABLE "county_public_safety" (
"County_ID" int,
"Name" text,
"Population" int,
"Police_officers" int,
"Residents_per_officer" int,
"Case_burden" int,
"Crime_rate" real,
"Police_force" text,
"Location" text,
PRIMARY KEY ("County_ID")
);
CREATE TABLE "city" (
"City_ID" int,
"County_ID" int,
"Name" text,
"White" real,
"Black" real,
"Amerindian" real,
"Asian" real,
"Multiracial" real,
"Hispanic" real,
PRIMARY KEY ("City_ID"),
FOREIGN KEY ("County_ID") REFERENCES "county_public_safety"("County_ID")
);
INSERT INTO  "county_public_safety" VALUES (1,"Abbotsford","128165","187","685","81","118","Abbotsford Police Department","East");
INSERT INTO  "city" VALUES (1,1,"Adjuntas","93.1","3.1","0.3","0.0","3.4","99.6");