which is better one big query or multiple small query?

Question

which is better and efficient? one big query then just process the fetched query in the php or from php function will just create a loop function that queries small data. Please consider also that the table can be big (thousands of raw). Thanks.

Comments table

id | parent | msg
---+--------+---------      
1  |   0    | hello   
2  |   1    | hi      
3  |   2    | whats up       
4  |   3    | yow       
5  |   1    | hellow   
6  |   2    | nice       
7  |   0    | great   

Expected output is this:

        Array
        (
            [0] => Array
                (
                    [id] => 1
                    [parent] => 0
                    [value] => hello
                    [child] => Array
                        (
                            [0] => Array
                                (
                                    [id] => 2
                                    [parent] => 1
                                    [value] => hi
                                    [child] => Array
                                        (
                                            [0] => Array
                                                (
                                                    [id] => 3
                                                    [parent] => 2
                                                    [value] => whats up
                                                    [child] => Array
                                                        (
                                                            [0] => Array
                                                                (
                                                                    [id] => 4
                                                                    [parent] => 3
                                                                    [value] => yow
                                                                )
                                                        )
                                                )
                                            [1] => Array
                                                (
                                                    [id] => 6
                                                    [parent] => 2
                                                    [value] => nice
                                                )
                                        )
                                )
                            [1] => Array
                                (
                                    [id] => 5
                                    [parent] => 1
                                    [value] => hellow
                                )
                        )
                )
            [1] => Array
                (
                     [id] => 7
                    [parent] => 0
                    [value] => great
                )

Answer 1

As a rule of thumb, the less queries the better.

This is a good question but this has been answered multiple times.

Is it better to return one big query or a few smaller ones?

Multiple small queries vs a single long query. Which one is more efficient?

One big query vs. many small ones?

Which one is faster single big query or few small queries?

What is faster, a big joined query with more PHP or multiple small selects with less PHP?

Should I use one big SQL Select statement or several small ones?

https://dba.stackexchange.com/questions/76973/what-is-faster-one-big-query-or-many-small-queries

https://dba.stackexchange.com/questions/35277/is-it-better-to-separate-a-big-query-into-multiple-smaller-queries