Mysql to Json. Can this be solved using MySQL? - php

Question

I have a MySQL query that will be converted to JSON and used in Obj C for each user with a specific id. I believe that this is a MySQL puzzle, but there may be an answer in JSON. I don't ask many questions, so I'll try to make it concise.
Here is a screen shot of values for one user. If you notice, the field_id may vary because not all info is required, so the id field will vary from 3 to 8 values for a given user_id:
I have to make a query where the results GROUP BY column1 (user_id), but only WHERE column2 (field_id) has the following values field_id='18' and field='19', Then (THE BIG PROBLEM) I need to populate the results in one GROUP with both values of column3 (value) so I can get results in one JSON object.
I already know how to convert to JSON for use in iOS, but I can only get it to give me results as two objects.
My current query
$query = "SELECT * FROM table1 WHERE field_id='18' OR field_id='19' ORDER BY user_id ";
Current Result
[{"id":"5","user_id":"461","field_id":"18","value":"1_MX4zNjcxNzM5Mn4x...","access":"0"},
{"id":"6","user_id":"461","field_id":"19","value":"T1==cGFydG5lcl9pZD0...","access":"0"},
{"id":"11","user_id":"463","field_id":"18","value":"1_MX4zNjcxNzM...","access":"0"},
{"id":"12","user_id":"463","field_id":"19","value":"T1==cGFydG5lcl9...","access":"0"}]
I need the two JSON objects with matching user_id fields as one object with results that differentiate field='18' value from field='19' value. Something like:
[{"id":"5","user_id":"461","field_id":"18","value18":"1_MX4zNjcxNzM5Mn4x...","value19":"T1==cGFydG5lcl9pZD0...","access":"0"},
{"id":"11","user_id":"463","field_id":"18","value18":"1_MX4zNjcxNzM...","value19":"T1==cGFydG5lcl9...","access":"0"}]
OR
[{"id":"5","user_id":"461","field_id='18'":"1_MX4zNjcxNzM5Mn4x...","field='19'":"T1==cGFydG5lcl9pZD0...","access":"0"},
{"id":"11","user_id":"463","field_id='18'":"1_MX4zNjcxNzM...","field='19'":"T1==cGFydG5lcl9...","access":"0"}]
THANKS...

Answer 1

I'm not 100% sure if this will work. I cannot easily try the JSON output of it. But what if you run a query like this?
SELECT id, user_id,
GROUP_CONCAT(field_id,':',value) field_id,
access
FROM table1 WHERE field_id='18' OR field_id='19'
GROUP BY user_id
ORDER BY user_id

Answer 2

You probably want to to look at handling this in PHP when reading in the result set.
So use your current query of
SELECT * FROM table1 WHERE field_id='18' OR field_id='19' ORDER BY user_id
But build result data object like this:
$results = array();
$i = -1;
$current_user_id = '';
while ($row = [YOUR MySQL FETCH MECHANISM HERE]) {
// determine if this record represents a new user id in the result set
// if so, we need to set up the user object and start another entry in top level array
if($current_user_id != $row['user_id']) {
// you have moved to a new user in the result set
// increment your array counter and set current user id
$i++; // will set value to 0 on first iteration
$current_user_id = $row['user_id'];
// build new array entry
$results[$i] = new stdClass();
$results[$i]->user_id = $current_user_id;
$results[$i]->fields = array();
}
// build field object for insertion
$field = new stdClass();
$field->field_id = $row['field_id'];
$field->value = $row['value'];
$results[$i]->fields[] = $field;
}
On encoding $results this would give you a JSON structure like this:
[
{
"user_id":"461",
"fields": [
{
"field_id":"18",
"value":"foobar"
},
{
"field_id":"19",
"value":"abcxyz"
}
]
},
...
]
This data structure is going to be more readily usable by consuming app than some solution which requires exploding concatenated field id/value strings. Also note that I have not included id field anywhere in data structure, as it has no meaning in this context. If you truly needed that id, you could add it as another property in the field object since that is where there is a one-to-one relationship (not with user_id).
Based on your comment, if the field value is known and you need to access it via field_id index, you can slightly modify what I have shown above to build index-able field listing rather than a simply array of objects:
$results = array();
$i = -1;
$current_user_id = '';
while ($row = [YOUR MySQL FETCH MECHANISM HERE]) {
// determine if this record represents a new user id in the result set
// if so, we need to set up the user object and start another entry in top level array
if($current_user_id != $row['user_id']) {
// you have moved to a new user in the result set
// increment your array counter and set current user id
$i++; // will set value to 0 on first iteration
$current_user_id = $row['user_id'];
// build new array entry
$results[$i] = new stdClass();
$results[$i]->user_id = $current_user_id;
$results[$i]->fields = array();
}
// insert field value at field_id index position
$results[$i]->fields[$row['field_id']] = $row['value'];
}
This would give you a JSON representation like this.
[
{
"user_id":"461",
"fields": {
"18":"foobar",
"19":"abcxyz"
}
},
...
]
This would allow easy look-up by client based on field id. Of course you may want to consider similar for user_id. From the user object you could just access fields->18 (or similar based on on client language syntax).