CODEWITHSUNDEEP
phpmysql
egg man
egg man

Reputation: 23

How to select every other result in this loop? [PHP]

I have this loop that outputs to a graph. Over time, the data in my 'history' table grows dramatically and I want to cut down on the amount being outputted onto the graph, by selecting every other result.

How can I do this with my code?

<?php

    $cdate = 0;   
    $counter = 0;

    $sql = "SELECT * FROM history WHERE time < '$ctime' ORDER BY time asc";
    $result = $conn->query($sql);

    if ($result->num_rows > 0) {
        while($row = $result->fetch_assoc()) {
            $cdate = ($row["time"]);

            $sql1 = "SELECT AVG(value) AS avgval FROM history WHERE time = '$cdate' AND time < '$ctime'";
            $result1 = $conn->query($sql1);

            if ($result1->num_rows > 0) {  
                while($row1 = $result1->fetch_assoc()) {   
                    $avgval = $row1["avgval"];
                    echo "[new Date((".($row["time"] * 1000).")), ".$avgval."],";    

                }  
            }
        }     
    }
?>

For example, if I have this in my table (history):

[id] --- [ticker] --- [value] --- [time]

1 --- Group1 --- 100 --- 730

2 --- Group 2 --- 200 --- 730

3 --- Group 1 --- 110 --- 740

4 --- Group 2 --- 235 --- 740

5 --- Group 1 --- 310 --- 750

6 --- Group 2 --- 485 --- 750

How can I just output the average of #1, #2 and the average of #5, #6 - ignoring #4 and #5?

Upvotes: 2

Views: 58

Answers (1)

Matt
Matt

Reputation: 1570

<?php
$cdate = 0;   
$counter = 0;

$sql = "SELECT * FROM history WHERE time < '$ctime' ORDER BY time asc";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $cdate = ($row["time"]);

        $sql1 = "SELECT AVG(value) AS avgval FROM history WHERE time = '$cdate' AND time < '$ctime'";
        $result1 = $conn->query($sql1);

        $i = 0; // incrementor
        if ($result1->num_rows > 0) {  
            while($row1 = $result1->fetch_assoc()) {   
                ++$i; // plus one
                if($i % 2 == 0) { // check if $i is even          
                    $avgval = $row1["avgval"];
                    echo "[new Date((".($row["time"] * 1000).")), ".$avgval."],";    
                }
            }  
        }
    }     
}
?>

Upvotes: 1

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