SQL SELECT和PHP检索速度使用单表VS加入两个表？

Question

I'm in the process of creating a table then display records. i want to display users height in 'inch' format but it will store it in 'cm' forma in users table. Now I want to know which way will give me faster result ?

Using JOIN

// to select records  
 SELECT *.u FROM, h.height_inch user as u join height as h on u.height_cm =h.height_cm 
 WHERE u.user_id = 2 AND ...;
//for display in php  
 foreach($all_records AS $key => $val) {
  echo $val['height_inch'];
  }

OR Single User table (Faster/slower than) :

 // to select records  
 SELECT * user WHERE u.user_id = 2 AND ...;
//for display in php  
 foreach($all_records AS $key => $val) {
   $height_in_cm = $val['height_inch']
   $height_in_inch= convert_to_inch($height_in_cm); //function for  convert height cm to inch..
    echo $height_in_inch;
  }

Answer 1

An even faster alternative would be to simply perform the arithmetic in SQL so you don't have to store fixed conversion data or iterate over the results.

SELECT height_cm, height_inches as (height_cm / 2.54) FROM table;