PHP函数用于处理MySQL无限和嵌套查询

Question

I've been asked by my colleague to make a PHP function to plug into our web application to handle an infinite amount of nested (looped) queries to make our lives much easier, without being worried about loosing the current and/or previous results.

Here is the code I came up after minutes, and it seems that it works fine, however I still have these questions:

1. Am I re-inventing the mysqli_prepare function?
2. Is it smart to handling these nested queries in this way?
3. What could be pros and cons of using the following approach?

The actual function:

function qn($query) {
    global $db;
    $rand_var = 'r' . mktime() . mt_rand();
    $$rand_var = $db->query($query);
    return $$rand_var;
}

and in action:

if (($db instanceof mysqli) != true) {
   $db = new mysqli(DB_ADDRESS, DB_USER, DB_PASS, DB_NAME);
}

$a = qn('SELECT DISTINCT ***');

while ($row_a = $a->fetch_assoc()) {
    // do some stuff
    $b = qn('SELECT ***' . $row_a['foo']);
    while ($row_b = $b->fetch_assoc()) {
        $c = qn('SELECT COUNT(id)' . $row_b['bar']);
        // keep going ...
    }
}

Note: SQL queries are sample.

Answer 1

Here you go: SafeMysql is what you're looking for and many, many more!

if (!($db instanceof safemysql)) {
   $db = new safemysql(...);
}

$a = $db->getCol('SELECT DISTINCT ***');
foreach ($a as $foo) {
    // do some stuff
    $b = $db->getAll('SELECT ***', $foo);
    foreach ($b as $row_b) {
        $c = $db->getOne(('SELECT COUNT(id)', $row_b['bar']);
         // keep going ...
    }
}

To answer your question

Am I re-inventing the mysqli_prepare function?

Definitely NO.
You're preparing nothing.

Is it smart to handling these nested queries in this way?

No. The probability of collision is pretty high. At least use microtime instead of mktime.

What could be pros and cons of using the following approach?

There a lot of cons

• no error handling
• no placeholders support
• messy code
• whole qn() function being useless. you can use $db->query() alone instead.

Also, Till Helge Helwig is absolutely right: all nested queries can (and should) be replaced with single query with join (and grouping).

Answer 2

The following code:

$rand_var = 'r' . mktime() . mt_rand();
$$rand_var = $db->query($query);
return $$rand_var;

could be simplified to

return $db->query($query);

Cause it just stores query result in local variable with unique name before returning it. This does not make much sense.