MySQL: Join (2 tables) vs single queries (1 table)

Question

In PHP, I have an array of 11 persons where just the ID of each person is given:

$persons = array(1, 3, 39, 72, 17, 20, 102, 99, 77, 2, 982);

In my MySQL database, there's a table containing detailed information about each person:

TABLE personInfo
 - ID (integer)
 - name (string)
 - birth date (timestamp)
 - weight (decimal)
 - ...

PROBLEM:

So now, I want to select the matching name for each ID in the PHP array. I can only imagine two solutions to do this:

1. for-loop:

foreach ($persons as $person) {
    $result = mysql_query("SELECT name FROM personInfo WHERE id = ".$person);
}

2. logical operator OR

$result = mysql_query("SELECT name FROM personInfo WHERE id = 1 OR id = 3 OR id = 39 OR ...");

Both solutions are slow, aren't they?

But if I had another MySQL table containing the IDs of the PHP array ...

TABLE ids
 - ID (integer)

... I could use a join to make a really fast MySQL query, right?

$result = mysql_query("SELECT a.ID, b.name FROM ids AS a JOIN personInfo AS b ON a.ID = b.ID");

QUESTION:

Is all this correct so far? If yes: Why is this so? The MySQL query is faster if I have a second table? With only one table it is incredibly slow? What is the fastest way to solve my problem (selecting the names matching the IDs of the PHP array)?

Answer 1

If you have lots of ids (several hundreds or more), feeding the values into a temporary table and joining it is actually faster.

You may want to read this article:

• Passing parameters in MySQL: IN list vs. temporary table