MYSQL_05_ JOIN

INNER JOIN

C.CategoryID 와 P.CategoryID가 같은 컬럼을 찾아서 JOIN해줌
SELECT * FROM Categories C
JOIN Products P 
  ON C.CategoryID = P.CategoryID; 
  
위와 비슷 
SELECT C.CategoryID, C.CategoryName, P.ProductName
FROM Categories C
JOIN Products P 
  ON C.CategoryID = P.CategoryID;