CODEWITHSUNDEEP
php
Tim C
Tim C

Reputation: 5714

PHP implode function explanation

I am relatively new to PHP. The textbook im working from covers PHP5.2 and mentions nothing of implode. The information im getting from PHP manual is a bit unclear to me. Im looking for a short clear explanation and example on implode

I know implode returns a string of the elements of its array but how is the following 2 exmples different, and why would you use one over the other:

example 1

$query = 'SELECT `name`, `position` 
        FROM `player_info` 
        WHERE `player_id` IN (' . implode(',', $player_ids) . ')';

example 2

 $result2 = mysql_query("SELECT `fixture_id`, `opponents` 
                         FROM `fixtures` ") or die (mysql_error());

Thank you

Upvotes: 0

Views: 344

Answers (5)

Duniyadnd
Duniyadnd

Reputation: 4043

I'm going to ignore the fact that you're using mysql_query() in your code - as that is a more vulnerable library in the PHP reportoire. When you get more comfortable, or if you can right away, use PDO.

To understand implode() you need to understand arrays(). I'm going with the assumption that you know what arrays are.

In SQL, when you use IN() - it's equivalent to multiple "OR"s.

e.g.

SELECT * FROM table t WHERE t.id IN ( 1,2,3 )

is essentially the same as:

SELECT * FROM table t WHERE t.id = '1' OR t.id = '2' OR t.id = '3' OR t.id = '3'

When you have an array in PHP - it will look like this:

$array = array ( 1 , 2 , 3 );

If you wanted to dump it into the SQL statement, it'll fail, because a query like:

SELECT * FROM table t WHERE t.id IN ( $array )

would output:

SELECT * FROM table t WHERE t.id IN ( Array )

What you want are the values within the array. That's where implode() comes in. Implode would create delimiter - which is equivalent to a consistent value that goes between each value in your array (in your example, a comma) and will output the necessary string that you need in SQL.

$array = array ( 1 , 2 , 3 );
$query = "SELECT * FROM table t WHERE t.id IN ( ".implode("," , $array)." ) ";

Is the same as:

$query = "SELECT * FROM table t WHERE t.id IN ( 1,2,3 ) ";

Hope that helps

Upvotes: 2

sybear
sybear

Reputation: 7784

implode creates a string from an array. You must have some basic understanding of array, before you start working with it.

Thus, if you have a set of same-type data you store it in arrays. The first parameter in array is a delimiter. Second - is the array.

$animals = ("cats", "dogs", "cows");
echo implode(" &", $animals) . " are animals" ;

Will produce: cats & dogs & cows are animals

In your first example, there is IN construction which can accept several parameters. Arrays are just suitable to work with it.

$player_ids = array(1,2,3);

"IN (".implode(", ", $player_ids).")" will result in IN (1, 2, 3)

Upvotes: 0

Niet the Dark Absol
Niet the Dark Absol

Reputation: 324650

Implode can be particularly useful for lists. Say you have an array of ingredients, you might echo implode("\n",$ingredients) to show them on their own lines.

In your first example, you need to be very careful. It will only work properly if $player_ids is an array of numbers. implode() by itself is perfectly secure, however improper use can leave gaping holes in your security. A more "correct" version of that code might look like this:

$query = "SELECT `name`, `position` FROM `player_info`
  WHERE `player_id` IN ('".implode("','",array_map("mysql_real_escape_string",$player_ids))."')";

The above code also handles the case where $player_ids is empty. In your code, it will result in a MySQL syntax error (IN () is not valid), whereas in this code it will simply look for IN (''), which will match no rows.

Another use for implode might be when packing numbers. Say you have an array of digits, you might implode("",$digits) to pack them into a single string (and str_split($string) to unpack them).

In short, there are many potential uses for this function, and generally it will be obvious when the function applies. Try not to think too hard about it ;)

Upvotes: 1

DonCallisto
DonCallisto

Reputation: 29922

Implode will take an array and transform it in a string where each element of original array will be separated by "first parameter" of implode function.

What do you mean with "secure"? I don't understand this question but I suppose that you are asking it because you seen implode() used into a db query (in the example). implode() has nothing to do with db query so no sql injection (*) and so on.

We should use it instead of loop over the whole array

(*) obviously you should pay attention of what array to implode is

Upvotes: 0

alandarev
alandarev

Reputation: 8635

Example 1 extracts players information of the players who's ID's are $player_ids. Second example extracts two columns without WHERE condition.

What is your question exactly? As long as you are 100% sure the $player_ids is an array of integers! then it is safe.

Upvotes: 0

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