|--column1--|--column2--|
|     0     |    1234   |
|     3     |    5678   |
-------------------------

A MySQL query took a while, but didn’t time out when the list of WHERE column2=’value’ was less than 7000, but it was just overwhelmed at 10,000. Okay, fine, time to go to phase two: in_array().
There was an existing array of values for column2, so I could simply pull a list of <3 from MySQL (quick) and then loop through (foreach) each of the results and check whether they are in_array() for the original source. If they were, just save them to a brand new array that I’ll use to work further through the problem. For clarification, that means that the system should go through 10,000+ iterations and check if each value is in_array(). If you had not already guessed, this was disastrous. In_Array() is very inefficient, and if you are dealing with an array that is more than 100 or so values, you’ll quickly learn this fact. So what to do? Use isset().
Isset(), as a function, is incredibly fast. It only checks whether something exists, and is a great way to check for whether something exists in an array. However, the trick is using isset() will look at the KEYS, while in_array() will look at the VALUES. Is that problem? Not if you build the original array as [value]=>value (set the KEY and VALUE the same). Now, as long as your values are valid keys and unique, this won’t be a problem. Then, you can use a foreach loop to check whether it is found in the original array. Here is some sample code:

$array_source = array('abc'=>'abc','def'=>'def','ghi'=>'ghi');
$array_results = array('xyz','ghi');
foreach ($array_results as $v){
  if (isset($array_source[$v])){ //fast
    $result[] = $v; //if found, save it to a fresh array
  }
}

What was the final result? The query, run 6 different times for 6 different data sets, went from a total execution time exceeding 2 minutes (MySQL), to not working at all (in_array), to 0.18 seconds. Yes, less than one second! That is the power for checking whether a value is set when comparing arrays. Isset() is even faster by a notable amount when compared to array_diff().

$string = "  \n Hello World!";
echo ltrim($string);

Hello World!

echo ltrim($string, " \nA..Ha..z!");
// All capital letters between A and H, all lowercase letters, exclamation point, space, and newline

World!

rtrim()

$string = "!Hello World42! \t\t";
echo rtrim($string);

!Hello World42!

echo rtrim($string, " \t!0..9");
// Range included is all numbers between 0 and 9, tab, space, and exclamation point.

!Hello World

Returns an array with they keys…

It should read:

Returns an array with the keys…

UPDATE table SET column1=’newvalue’,column2=’nextvalue’ WHERE column3=’value’

Returns: 1 if matched, 0 if no match, and FALSE on error.

It is still a work in progress, but the new PHP Code Checker will not execute your code, simply scan it as a string and run a battery of tests to find these mistakes. It is only a few weeks and less than 10 hours of work in it so far, but it is already at version 0.2 and is ready to help you. There is more coming soon, so keep tabs on the site and I hope it helps you deal with those tough code problems!

Photo courtesy of Zach Klein

I could attempt to explain this, but someone has already done a very good job of this, so I’d rather just provide a link to their content. The post is from the author of “High Performance MySQL”, Baron Schwartz, and covers writing an SQL Exclusion Join. The key area of interest is the section on LEFT OUTER joins. He offers this example query:

SELECT apples.Variety
FROM apples
    LEFT OUTER JOIN oranges
        ON apples.Price = oranges.Price
WHERE oranges.Price IS NULL

When in doubt, find someone smarter to answer the question for you. Thanks Baron!

function preprint($arr){
  echo '< pre>'.print_r($arr).'< /pre>';
}
$array = scandir(getcwd());
preprint($array); // nicely formatted display of the array

 
Of course, you can skip the print/echo portion if you don’t wish to display the contents and just use the array to perform other checks, but you get the idea.

// file.txt contains the sentence: Hello World!
$filename = 'file.txt';
$file = fopen($filename, 'r');
$string = fread( $file, filesize($filename) );
var_dump($string);
// file.txt now contains at the end: Hello World!

You’ll notice that this is the same tip as fread() and doesn’t belong. It should be considered ‘removed’.

pg. 162

preg_match_all: 157-158

pg. 161

array_combine: 73
array_key_exists: 79-80