PHP if condition for adding and removing without completely rebuilding - php

Question

I'm creating a PostgreSQL table column management tool to quickly add, remove and rearrange columns in tables. Thus far it is working great in simple scenarios where I simply append a column to the end or remove an existing column. Each of my if conditions call other functions to append a new column, delete an existing column or to rebuild the table as a whole; these functions work great as far as I can currently test.
How do I create an if condition where I'll call both the append function and the delete function instead of the rebuild function?
I have several arrays to help me determine the logic though I'm having trouble getting it worked out. Here are the arrays of column names and again in this scenario I should not be calling the rebuild function, need to call the append function and the delete function.
In this scenario all I'm going to do is delete the column id_2 and add the column id_4 so there is no need to rearrange the order or columns.
$columns_db - The columns as they exist in the PostgreSQL database.
Array
(
[0] => id
[1] => id_1
[2] => id_2
[3] => id_3
)
$columns_updated - The columns in the database that we're going to keep.
Array
(
[0] => id
[1] => id_2
[2] => id_3
)
$columns_submitted - The final way the columns should appear when all is done,
Array
(
[0] => id
[1] => id_2
[2] => id_3
[3] => id_4
)
$columns_slice
$columns_slice = array_slice($columns_submitted,0,(count($columns_updated) - 1),true);
Array
(
[0] => id
[1] => id_2
)
$columns_remove - The column(s) that will be dropped.
Array
(
[1] => id_1
)
$columns_append - The column(s) that will be created.
Array
(
[id_4] => bigint
)

Answer 1

Perform column deletions first
implode column list after deletions ($before = implode($columns_updated);)
implode column list after additions ($after = implode($columns_submitted))
if (strpos($after, $before) === 0) { /* the additions are at the end */ }
Make sure you use the === operator.
As a one-liner:
$rebuild = (strpos(implode($columns_submitted), implode($columns_updated)) !== 0);

Answer 2

I generally prefer straight forward if / else if conditions though it seemed that it would be simply too wildly convoluted to maintain. #AbraCadaver had the good sense to keep the add/remove detection separate which I adapted (would have up-voted if it wasn't deleted). I've tested about a dozen tricky combinations and haven't been able to find any false-positives. Here is the debug version I used to help visualize the logic:
$rebuild = 0;
foreach ($columns_append as $k1 => $v1)
{
//echo '<div class="clear">k1 = '.$k1.'</div>';
if (in_array($k1,$columns_slice)) {$rebuild = 1; break;}
else
{
$columns_submitted_key = array_search($k1,$columns_submitted);
//echo '<div class="clear">columns_submitted_key: '.$columns_submitted_key.', $columns_updated count = '.count($columns_updated).'</div>';
if ($columns_submitted_key<count($columns_updated)) {$rebuild = 1; break;}//echo '<div class="error">Yeah, rebuild here.</div>';
}
}
if ($rebuild>0) {echo '<div class="clear">1, rebuild.</div>';}
else
{
if (count($columns_append)>0) {echo '<div class="clear">2,append</div>';}
if (count($columns_remove)>0) {echo '<div class="clear">3,delete</div>';}
}