CREATE TABLE table_204_258 (id NUMBER, "location" CLOB, "frequency" NUMBER, "call sign" CLOB, "network" CLOB, "call sign meaning" CLOB)

which frequency has the most stations ?
SELECT "frequency" FROM table_204_258 GROUP BY "frequency" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "frequency" FROM "table_204_258" GROUP BY "frequency" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY