CREATE TABLE table_17975 ("Value" CLOB, "Diameter" CLOB, "Thickness" CLOB, "Mass" CLOB, "Composition" CLOB, "Edge" CLOB, "Obverse" CLOB, "Reverse" CLOB, "first minting" FLOAT, "issue" CLOB, "withdrawal" CLOB, "lapse" CLOB)

How many coins have a diameter of 23mm?
SELECT COUNT("Reverse") FROM table_17975 WHERE "Diameter" = '23mm'
SELECT COUNT("Reverse") FROM "table_17975" WHERE "Diameter" = '23mm'