CREATE TABLE table_74223 ("No." FLOAT, "Name" TEXT, "Place of Birth" TEXT, "Date of Birth" TEXT, "Previous Club" TEXT, "Date Joined" TEXT, "Fee" TEXT, "Contract Expiry" TEXT)

how many date of birts are if the previous club is chelsea
SELECT COUNT("Date of Birth") FROM table_74223 WHERE "Previous Club" = 'Chelsea'
SELECT COUNT("Date of Birth") FROM "table_74223" WHERE "Previous Club" = 'Chelsea'