How to parse second level of json php - php

Question

I have a json like this:
[{"a":"1", "b":"2"},{"a":"4", "b":"5"},{"a":"15", "b":"2"}]
I want to get in php each row for update my database. I don't know the number of second level json are. Sometimes will be 1, sometimes 2 and sometimes more.
I thought, I could read it doing something like this:
$json = file_get_contents('php://input');
$json_post = json_decode($json, true);
$i = 0;
while(isset($json_post[$i])){
//Bla bla
$i++;
}
I have used many times json file in php but always, just one level. This is my first time with more than one.
But I can't. I know, because I checked, that in $json I have the complete json file.

Answer 1

You need to reference the subkey in your array:
$json = file_get_contents('php://input');
$json_post = json_decode($json, true);
$i = 0;
while(isset($json_post[$i])){
echo $json_post[$i]["a"];
// or
echo $json_post[$i][0];
$i++;
}
More docs can be found here: http://php.net/manual/en/language.types.array.php
And a similar question here: PHP reference specific key and value within multidimensional array

Answer 2

i'd use foreach:
foreach($json_post as $key => $value) {
echo $value;
}

Answer 3

$j = '[{"a":"1", "b":"2"},{"a":"4", "b":"5"},{"a":"15", "b":"2"}]';
$decoded = json_decode($j, true);
//var_dump($decoded);
foreach ($decoded as $key => $post) {
$valueOfA = $post['a'];
$valueOfB = $post['b'];
}