Calculate age: PHP vs MySQL, which method is better? - php

Question

I have around 500,000 records of personal profile in MySQL database containing a birthdate column (dob). Since I had to get the ages for each profile, I needed to calculate it dynamically which I can either do via PHP (date_diff(date_create($dob), date_create('today'))->y) or through SQL ('SELECT TIMESTAMPDIFF(YEAR, dob, CURDATE()) AS age').
Which of the two is faster or more preferred especially if I have hundreds of thousands of rows?

Answer 1

In general, the best approach is to do such calculations on the server.
The ideal approach would be to use a generated column. This has been available since MySQL 5.7.5, and would be expressed as:
alter table t add age unsigned as
(TIMESTAMPDIFF(YEAR, dob, CURDATE()));
Alas, you can only use deterministic functions for generated columns. curdate() and now() are not deterministic, because their values can change with each call.
The next best thing is to use a view:
create view v_t as
select t.*,
TIMESTAMPDIFF(YEAR, dob, CURDATE())
from t;
Then, when you query the view, you'll have the age. This is true no matter where you query it. And it is the same logic everywhere.
The only caveat to doing the calculation on the server is that it uses server time, rather than local application time. If that is an issue, then that is a strong argument for doing the calculation locally.

Answer 2

Here is a test:
Create a table with 100K random dates
drop table if exists birthdays;
create table birthdays (
id int auto_increment primary key,
dob date
);
insert into birthdays (dob)
select '1950-01-01' + interval floor(rand(1)*68*365) day as dob
from information_schema.COLUMNS c1
, information_schema.COLUMNS c2
, information_schema.COLUMNS c3
limit 100000
;
Run this PHP script
<?php
header('Content-type: text/plain');
$db = new PDO("mysql:host=localhost;dbname=test", "test","");
### SQL
$starttime = microtime(true);
$stmt = $db->query("SELECT id, dob, TIMESTAMPDIFF(YEAR, dob, CURDATE()) AS age FROM birthdays");
$data = $stmt->fetchAll(PDO::FETCH_OBJ);
$runtime = microtime(true) - $starttime;
echo "SQL: $runtime \n";
### PHP
$starttime = microtime(true);
$stmt = $db->query("SELECT id, dob FROM birthdays");
$data = $stmt->fetchAll(PDO::FETCH_OBJ);
foreach ($data as $row) {
$row->age = date_diff(date_create($row->dob), date_create('today'))->y;
}
$runtime = microtime(true) - $starttime;
echo "PHP: $runtime \n";
Result:
SQL: 0.19094109535217
PHP: 1.203684091568
It looks like the SQL solution is 6 times faster. But that is not quite true. If we remove the code which calculates the age from both solutions, we will get something like 0.1653790473938. That means the overhead for SQL is 0.025 sec, while for PHP it is 1.038 sec. So SQL is 40 times faster in this test.
Note: There are faster ways to calculate the age in PHP. For example
$d = date('Y-m-d');
$row->age = substr($d, 0, 4) - substr($row->dob, 0, 4) - (substr($row->dob, 5) > substr($d, 5) ? 1 : 0);
is like four times faster - while date('Y-m-d') consumes more than 80% of the time. If you find a way to avoid any date function, you might get close to the performance of MySQL.

Answer 3

if you want get all 500,000 records you should do this in MySql because performance is better than PHP
but, if you want get some of that data (for example 10 records) , do that with PHP it's better to handle. and performance not different