PHP: Merge/delete arrays with same subkeys

I'm writing a database class for my site based on a fluent interface. First, I collect all the meaningful terms then put them into the "stack", which is basically an array. Then, I sort them in order that they would appear in an actual SQL query.

const stmt_select = 1;

const stmt_insert = 2;

const stmt_delete = 3;



const sql_select = 10;

const sql_from = 11;

const sql_into = 12;

const sql_where = 13;

const sql_join = 14;

const sql_group = 15;

const sql_order = 16;

const sql_limit = 17;

For example, the query below (although in a total rubbish order, and purposely trying to throw the class off):

Query::Select('name', 'age', 'height')

    ->Order('a')

    ->From('table')

    ->From('asd')

    ->Group('a')

    ->Execute();

.. produces:

Array

(

    [0] => Array

        (

            [0] => 10

            [1] => Array

                (

                    [0] => name

                    [1] => age

                    [2] => height

                )



        )



    [1] => Array

        (

            [0] => 11

            [1] => asd

        )



    [2] => Array

        (

            [0] => 11

            [1] => table

        )



    [3] => Array

        (

            [0] => 15

            [1] => a

        )



    [4] => Array

        (

            [0] => 15

            [1] => a

        )



)

The problem I have is that some array members I want to merge together (for example multiple ->Selects()/->Where() clauses) and some array members I want to delete entirely if there are multiple instances because it isn't possible for there to be more than one (for example ->Limit(), ->Order()), however I'm not entirely sure what the easiest way to do this is.

I was thinking something along the lines of a function I could call for each subkey;

DeleteDuplicates(sql_order);

Merge(sql_select);

Not sure how to write these without a massive performance hit per query.

Regards, kvanberendonck