json DataTable in googlecharts - php

Question

I am having a bit of trouble getting the proper format of json string.
I have a database table that looks something like this:
Table Columns: emp month sales
Table rows: Bob 1 100
Bob 2 150
Jane 1 125
Jane 2 130
Mary 1 110
Mary 2 130
Within drawChart(), I can create something like this statically:
var data = google.visualization.arrayToDataTable([
['Month', 'Bob', 'Jane', 'Mary],
['Jan', 100, 125, 110],
['Feb', 150, 130, 130]
]);
In the end, the json string needs to look like this:
{"cols":[{"label":"Month","type":"string"},
{"label":"Bob","type":"number"},
{"label":"Jane","type":"number"},
{"label":"Mary","type":"number"}],
"rows":[{"c":[{"v":100},{"v":125},{"v":110}]},
{"c":[{"v":150},{"v":130},{"v":130}]}]}
But I am having trouble pulling from the table to come up with proper json formatting that is equivalent to the above. I am following the steps from here... PHP MySQL Google Chart JSON - Complete Example
But that example is only for a single data set. if you were to add multiple weeks instead of having just one data set, how do run the query?

Answer 1

To get your data in the format you want, you have to pivot your data. Some databases support pivotting, but others like MySQL don't. If you are stuck without pivot support, then you have to resort to trickery to make it happen. Here's one way you could do it:
SELECT
month,
SUM(if(employee = "Bob", sales, 0)) AS Bob,
SUM(if(employee = "Jane", sales, 0)) AS Jane,
SUM(if(employee = "Mary", sales, 0)) AS Mary
FROM myTable
GROUP BY month
This requires that you know ahead of time what the employee names are so that you can write the SQL statement (either when you write the code, or you could pull them from another SQL query and write a dynamic SQL query).

Answer 2

Asgallent, thank you. Your response gave me the direction I needed. I was able to do it all dynamically via SQL. I made two queries: 1 to the "saleperson" table to get the names, and then another to pivot the data as you suggested. For anyone else that might find this helpful, here is the code I have.
The queries (Note: I am using codeigniter):
$sp_qry = $this->db->query('select * from salespeople');
$qryString="";
foreach ($sp_qry->result_array() as $row)
{
$qryString.= ",SUM( IF( `salespeople_id` =" . $row['salespeople_id'] . ", `num_sold` , 0 ) ) AS " . $row['name'];
}
$qry= "SELECT `month` " . $qryString . " FROM `product_sales`
GROUP BY `month`";
$query = $this->db->query($qry);
return $query->result_array();
and in my viewing page
$rows = array();
$table = array();
$cols = array();
$cols[] = array('label' => 'Month', 'type' => 'string');
foreach ($salespeople as $sp)
{
$cols[] = array('label' => $sp['name'], 'type' => 'number');
}
$table['cols'] = $cols;
foreach ($sales as $chart_item)
{
$tmp=array();
$tmp[] = array('v' => (string) $chart_item['month']);
foreach ($salespeople as $sp)
{
$name=$sp['name'];
$tmp[] = array('v' => (int) $chart_item[$name]);
}
$rows[] = array('c' => $tmp);
}
$table['rows'] = $rows;
$jsonTable = json_encode($table);