MySQL - DATE_ADD month interval by each month - mysql

Question

I have written a function below to give me the number of jobs an employee has done in a particular 30 day period (each ID in the 'jobs column' of the table represents 1 job).
the function work fine if I only want to look back 4 week. the problem however is that I want the count to start at the beginning of each month. for example, if a person views the records on the 10th December 2013 I need the records to show all the work for December (but not the records for the preceding 30 days).
Below is my function:
$interval_1month = 'interval 4 WEEK';
function statsHowMuchWorkDoneByStaff ($staff_id, $timeInterval)
{
global $dbc;
$select = " SELECT
COUNT(job_id) AS totalnumberWork ";
$from = " FROM
staffwork
";
$where = " WHERE
staff_id = $staff_id
AND
FROM_UNIXTIME(entrytime) >= now() - $timeInterval";
$query = $select.$from. $where;
$result = mysqli_query ($dbc, $query)
or trigger_error("Query: $query\n<br />MySQL Error: " . mysqli_error($dbc));
if(mysqli_num_rows($result))
{
$row = mysqli_fetch_array ($result, MYSQLI_ASSOC);
$result = safe_output($row['totalnumbernewcontacts']) ;
return $result ;
}
else
{
return false;
}
}
Any advise on how to proceed would be greatly appreciated.
UPDATE: here is my datatable:
CREATE TABLE staffwork(
staff_id MEDIUMINT UNSIGNED NOT NULL,
job_id MEDIUMINT UNSIGNED NOT NULL,
data_table VARCHAR (65) NOT NULL,
entrytime int(11) NOT NULL,
INDEX message (staff_id)
);

Answer 1

If I understand correctly and you want to calculate COUNT(job_id) for a specific month by supplying any date of that month as a parameter, then you can do it this way
SELECT COUNT(job_id) total
FROM staffwork
WHERE staff_id = 1
AND entrytime >= UNIX_TIMESTAMP(LAST_DAY('2013-12-10') + INTERVAL 1 DAY - INTERVAL 1 MONTH)
AND entrytime < UNIX_TIMESTAMP(LAST_DAY('2013-12-10') + INTERVAL 1 DAY)
Note: This query is index friendly because it doesn't convert entrytime to datetime but rather convert range values (which are constants for the query) to unix time. Make sure that you have indices on entrytime and staff_id to be able to take advantage of that.
Here is SQLFiddle demo
And while you're at it consider to learn and use prepared statements instead of interpolating query strings leaving your code vulnerable for sql injections.
That being said your php function might look like this
function statsWorkDoneByStaffMember($staff_id, $month) {
global $dbc;
$sql = "
SELECT COUNT(job_id) total
FROM staffwork
WHERE staff_id = ?
AND entrytime >= UNIX_TIMESTAMP(LAST_DAY(?) + INTERVAL 1 DAY - INTERVAL 1 MONTH)
AND entrytime < UNIX_TIMESTAMP(LAST_DAY(?) + INTERVAL 1 DAY)
";
$stmt = $dbc->prepare($sql);
if (!$stmt) {
trigger_error('Prepare failed: ' . $dbc->error);
}
$stmt->bind_param('iss', $staff_id, $month, $month);
if(!$stmt->execute()) {
trigger_error('Execute failed: ' . $dbc->error);
}
$stmt->bind_result($result);
$stmt->fetch();
$stmt->close();
return $result;
}
Sample usage:
$dbc = new mysqli('localhost', 'user', 'password', 'dbname');
$staff_id = 1;
//Get the number of job_id for the current month
$total = statsWorkDoneByStaffMember($staff_id, date('Y-m-d'));
//Get the number of job_id for a specific month
$total = statsWorkDoneByStaffMember($staff_id, '2013-07-01');