Which is faster in MySQL? Joining 2 tables or calling table2 on iterative result row of table1?

Question

Hi please suggest to me which approach is better to use while retrieving data from two tables.

1.

List<xObjectType> result1 = DB.Query("SELECT * FROM table1");
for(int i = 0; i < result1.size(); i++){
    xObjectType tempObj = result1.get(0);
    yObjectType result2 = DB.Query("SELECT * from table2 WHERE table2.z = tempObj.x");
    // use tempObj and tempObj and use them.
}

List<xyCustomObjectType> result = DB.Query("SELECT * FROM table1 JOIN table2 WHERE table1.x = table2.z");
for(int i = 0; i < result.size(); i++){
    xyCustomObjectType tempObj = result.get(0);
    // use tempObj and write business logic.
 } 

  ResultSet rSet = DB.executeQuery("SELECT * FROM table1 JOIN table2 WHERE table1.x = table2.z");
  while(rSet.next()){
     xyCustomObjectType tempObj = result.get(0);
     // Fetch the results and perform operations
  }

Answer 1

It is best to use a single custom query to retrieve data from the database