MySQL Query with dynamic column name - mysql

Question

I have a source table with these columns:
I also have a destination table like this:
The destination table has 1440 rows, with the minute column filled in (1 row for each minute in the day).
For each row in the source table, I need to fill in a "1" in the destination table for the appropriate channel (there are 10 channels total), for every minute between the StartTime and FinishTime.
I'm just doing this in MySQL Workbench (it's a one-time query). What is my beast approach?
Thanks,
-Scott

Answer 1

Pseudo-code:
SELECT DISTINCT ChannelNumber
FROM source
while ($row = fetch_assoc()) {
$channel_col = 'ch'.$row['ChannelNumber']
$sql = "
UPDATE destination
JOIN source ON StartTime = destination.minutes
AND source.ChannelNumber = $row[ChannelNumber]
SET destination.$channel_col = 1
";
query($sql);
}
Normally you have to be concerned about dynamically creating a string which becomes an SQL query to avoid SQL injection, but since all the data is coming from within your database it shouldn't be a problem.

Answer 2

Here is an MySQL solution:
CREATE PROCEDURE PopulateDestinationTable()
BEGIN
DECLARE i INT DEFAULT 0;
DECLARE n INT DEFAULT 0;
DECLARE CNumber INT DEFAULT 0;
DECLARE STime INT DEFAULT 0;
DECLARE FTime INT DEFAULT 0;
SELECT COUNT(*) FROM SourceTable INTO n;
SET i = 0;
WHILE i < n DO
SELECT ChanelNumber FROM SourceTable LIMIT i, 1 INTO CNumber;
SELECT StartTime FROM SourceTable LIMIT i, 1 INTO STime;
SELECT FinishTime FROM SourceTable LIMIT i, 1 INTO FTime;
SET #stat1 = CONCAT('UPDATE DestinationTable
SET ', CONCAT('Ch', CNumber), ' = 1 WHERE minutes BETWEEN ? AND ?');
PREPARE statement FROM #stat1;
SET #p1 = STime;
SET #p2 = FTime;
EXECUTE statement USING #p1, #p2;
SET i = i + 1;
END WHILE;
END$$
P.S. Don't forget to change Delimiter when create stored procedure :)

Answer 3

I modified the PHP code from #peter-bowers to this and got it to work:
<?php
$mysqli = new mysqli("ip", "user", "pass", "db");
if ($mysqli->connect_errno) {
echo "Failed to connect to MySQL: (" . $mysqli->connect_errno . ") " . $mysqli->connect_error;
}
echo $mysqli->host_info . "\n";
$res = $mysqli->query("update scott_test set Ch1 = null, Ch2 = null, Ch3 = null, Ch4 = null, Ch5 = null, Ch6 = null, Ch7 = null, Ch8 = null, Ch9 = null, Ch10 = null");
$res = $mysqli->query("SELECT TIMESTAMPDIFF(MINUTE,DATE(TimeReceived),TimeReceived) AS StartTime,
CEIL(FaxDuration/60)+ TIMESTAMPDIFF(MINUTE,DATE(TimeReceived),TimeReceived) AS FinishTime,
ChannelNumber
FROM
fax_received
WHERE
DATE(TimeReceived) = DATE((NOW() - INTERVAL 3 DAY))");
while ($row = $res->fetch_assoc()) {
$channel_col = 'ch'.$row['ChannelNumber'];
$start_min = $row['StartTime'];
$end_min = $row['FinishTime'];
$sql = "UPDATE scott_test
SET $channel_col = 1
WHERE minutes between ($start_min, $end_min);
$mysqli->query($sql);
}
?>