A bag of random php/mysql related questions.

[Paul_help_]

Hi guys.

I am currently in the process of reading a php book and along the way I have stumbled across some things I need help understanding (listed below).

1) In the book I am reading, I have been learning about the 'command line tool' to communicate with MYSQL. In the book it states:

If you don ’ t fancy typing all these lines directly into the MySQL command - line tool, you can create a text
file — say, book_club.sql and enter the lines in there. Save the file in the same folder as you run the MySQL command - line tool from.

The thing is, I have tried to find the location of the 'command line tool' application on my computer, and to no avail. I use a laptop pc and my operating system is windows 7.
Do you know how I can find the location of the 'command line tool' so I can store an sql file from that same location, like it states in the above extract?

2) In the book I am reading, I came across the following extract:

PRIMARY KEY (memberId, pageUrl)

This was at the bottom of an sql 'create table' command.
The thing is, I was led to believe that you can only specify 'one' primary key per table.
Does the above mean that the two columns: 'memberId' and 'pageUrl' will, combined, make up one primary key?

3) Below is another extract from the book I am reading:

username VARCHAR(30) BINARY NOT NULL UNIQUE,

This is just simply a declaration of a column in a table I have been studying in the book I am reading.

I am aware of what 'BINARY' and 'UNIQUE' are for (in this context). In the book it states that using BINARY (above) will cause the field to be case-sensitive. The thing I need to ask is: surely 'UNIQUE' on its own would be enough to render the field case-sensitive? Or is UNIQUE not case sensitive? As, it doesn't actually say anything in the book.

4) In the book I am reading, there is an extract that states:

In a live server environment, you should store the file containing your database username and password
outside your document root folder, if possible, to avoid any chance of the username and password being
viewed by a visitor to the site.

How on earth could you store something outside your document root folder on a live server? Surely everything regarding your website needs to be in there in order for everything to work?

5) In the book I am reading, I have been studying some code, which builds an application. And the application makes great use of 'require_once()' because there are some class files (in the application) that are common to a lot of the files that make up the application. Obviously, this saves duplicating code over and over. Now to explain what it is I am unsure of - Some of the documents will use 'require_once()' on one file, and that file will use require once on another file. This 'top level' document will then be able to access the document that is required by the document it is requiring. But for some reason it seems like you can only take this so far.

Analyzing the code in my book, it seems like you cannot require something that requires something, that requires something.

If you do this, the top level cannot seem to access the bottom level (if you understand what I mean).

It seems like you can only go as far as 2 levels before require_once loses its effect and you have to use 'require_once()' again to include the bottommost file.

Am I correct in thinking this?

Paul.

[laserlight]

Paul help! wrote:

Do you know how I can find the location of the 'command line tool' so I can store an sql file from that same location, like it states in the above extract?

A quick search of the Web brings up this MySQL documentation page on the MySQL Installation Layout on Microsoft Windows. From there, you should be able to find the binary for mysql — The MySQL Command-Line Tool.

Paul help! wrote:

Does the above mean that the two columns: 'memberId' and 'pageUrl' will, combined, make up one primary key?

Yes.

Paul help! wrote:

I am aware of what 'BINARY' and 'UNIQUE' are for (in this context). In the book it states that using BINARY (above) will cause the field to be case-sensitive. The thing I need to ask is: surely 'UNIQUE' on its own would be enough to render the field case-sensitive? Or is UNIQUE not case sensitive?

No, UNIQUE declares that the fields in that column shall be unique. Put it this way: suppose that you consider "AB" and "ab" to be not equal. Then by saying that you only allow unique values, you would permit both "AB" and "ab". But suppose that you consider "AB" and "ab" to be equal. Then by saying that you only allow unique values, you would not permit both "AB" and "ab". Yet notice that whether or not you want to allow unique values, you made a determination as to whether "AB" and "ab" are equal.

You might want to read:
The BINARY and VARBINARY Types (the paragraph contrasting with CHAR BINARY and VARCHAR BINARY)
Case Sensitivity in String Searches

Paul help! wrote:

How on earth could you store something outside your document root folder on a live server? Surely everything regarding your website needs to be in there in order for everything to work?

The "document root folder" refers to the root of the directory tree that constitutes the public facing website. One common convention is to name it public_html. Your web host might allow you to place files in the parent directory of this directory, and doing so would hence be storing them outside of the document root folder.

[dalecosp]

Paul help!;11053535 wrote:

Hi guys.

I am currently in the process of reading a php book and along the way I have stumbled across some things I need help understanding (listed below).

1) In the book I am reading, I have been learning about the 'command line tool' to communicate with MYSQL. In the book it states:

The thing is, I have tried to find the location of the 'command line tool' application on my computer, and to no avail. I use a laptop pc and my operating system is windows 7.
Do you know how I can find the location of the 'command line tool' so I can store an sql file from that same location, like it states in the above extract?

I'm not aware of if, or whether, a MySQL installation on Windows includes a CLI tool. You might check your $PATH and look in the installation folder for an executable and try running it. If I'm stuck using Windows as my only way to access a MySQL server, I typically install HeidiSQL.

2) In the book I am reading, I came across the following extract:

This was at the bottom of an sql 'create table' command.
The thing is, I was led to believe that you can only specify 'one' primary key per table.
Does the above mean that the two columns: 'memberId' and 'pageUrl' will, combined, make up one primary key?

Yes.

3) Below is another extract from the book I am reading:

This is just simply a declaration of a column in a table I have been studying in the book I am reading.

I am aware of what 'BINARY' and 'UNIQUE' are for (in this context). In the book it states that using BINARY (above) will cause the field to be case-sensitive. The thing I need to ask is: surely 'UNIQUE' on its own would be enough to render the field case-sensitive? Or is UNIQUE not case sensitive? As, it doesn't actually say anything in the book.

I've actually not considered this before, but Alex Stetsensko has...

4) In the book I am reading, there is an extract that states:

How on earth could you store something outside your document root folder on a live server? Surely everything regarding your website needs to be in there in order for everything to work?

I think that you misunderstand "document root". In Apache, for example, and probably with most webserver software, you assign the DocumentRoot to be a specific folder on the server, and the IndexFile in that folder will be the page served when you call for the site's basic URL (typically this is index.html or index.php and you can see this file at www.yoursite.com/). There's nothing about DocumentRoot that means PHP can't read a different directory ... say, for example, your $HOME directory, or "/tmp".

5) In the book I am reading, I have been studying some code, which builds an application. And the application makes great use of 'require_once()' because there are some class files (in the application) that are common to a lot of the files that make up the application. Obviously, this saves duplicating code over and over. Now to explain what it is I am unsure of - Some of the documents will use 'require_once()' on one file, and that file will use require once on another file. This 'top level' document will then be able to access the document that is required by the document it is requiring. But for some reason it seems like you can only take this so far.

Analyzing the code in my book, it seems like you cannot require something that requires something, that requires something.

If you do this, the top level cannot seem to access the bottom level (if you understand what I mean).

It seems like you can only go as far as 2 levels before require_once loses its effect and you have to use 'require_once()' again to include the bottommost file.

Am I correct in thinking this?

Paul.

I don't actually know this one. However, testing indicates you're incorrect in your assumption:

[594] Tue 09.Feb.2016 11:19:31
[admin@forms][/tmp] cat foo.php bar.php baz.php qux.php quux.php
<?php

require_once("bar.php");

<?php

require_once("baz.php");

<?php

require_once("qux.php");

<?php

require_once("quux.php");

<?php

echo "\nQUUUUUUUUXXXXXXXXXXXXXXXXX...\n";
                                                                                                                                                                                                                                             [595] Tue 09.Feb.2016 11:19:46
[admin@forms][/tmp] php foo.php

QUUUUUUUUXXXXXXXXXXXXXXXXX...

Here you can see 5 levels of nested require_once() calls. A likely cause for any errors you might see using such a strategy is whether or not the path to the required file is appropriately designated.

HTH,

[Paul_help_]

Thanks.

So, refering back to my question 'number 2'.

If the following:

PRIMARY KEY (memberId, pageUrl)

... makes up one primary key,, then how would I refer to it later on down the line?

Would I need to specify both the 'memberId' and 'pageUrl' columns? Or just one of them?

Also, I don't know if I explained my question 'number 5 too well'.

To further illustrate what i mean, I have 4 hypohetical files below:

file 1:

file1.php

file 2:

file2.php
require_once( file1.php )

file 3:

file3.php
require_once( file2.php )

file 4:

file4.php
require_once( file3.php )

Now above, each file requires the previous file. What I was trying to explain in my original question was that - file 4 required file 3 and was thereby able access it's contents, and it could also access the contents of the file that file 3 required (file 2),, but from what i have found, it doesn't seem to go any further than this. In other words, if i wanted to access file 1, I would have to specify another require_once in file 4, like so:

file 4:

file4.php
require_once( file3.php )
require_once( file1.php )

.. is this correct logic?

And, refering back to my question 'number 3' - you are telling me that UNIQUE is not case sensitive?

Paul.

[laserlight]

Paul help! wrote:

.. makes up one primary key,, then how would I refer to it later on down the line?

Would I need to specify both the 'memberId' and 'pageUrl' columns? Or just one of them?

You could specify either one of them, but if you want to access the table by primary key, then your WHERE clause must include both of them.

That said, do you really need such a primary key? I prefer just having a column of autoincrementing integers designated as the primary key. You can declare a non-null unique index on memberId and pageUrl along with this primary key.

Paul help! wrote:

And, refering back to my question 'number 3' - you are telling me that UNIQUE is not case sensitive?

The concept of uniqueness is orthogonal to the concept of case sensitivity. UNIQUE is case sensitive if the comparison used is case sensitive. UNIQUE is not case sensitive if the comparison used is not case sensitive. Did you read the documentation that I linked?

[dalecosp]

Paul help!;11053567 wrote:

Now above, each file requires the previous file. What I was trying to explain in my original question was that - file 4 required file 3 and was thereby able access it's contents, and it could also access the contents of the file that file 3 required (file 2),, but from what i have found, it doesn't seem to go any further than this. In other words, if i wanted to access file 1, I would have to specify another require_once in file 4, like so:

.. is this correct logic?

Paul.

I cannot produce an example that matches your observation. Perhaps OS and PHP versions are different? Although PHP shouldn't have changed this.

Again, here's another set of files, reverse dependencies, as you show, depth of "4", and file4.php has access to the content of file1.php:

[778] Wed 10.Feb.2016 13:30:42
[admin@forms][/tmp] cat file1.php file2.php file3.php file4.php

<?php

$a = "one";

<?php

require_once("file1.php");

$b = "two";

<?php

require_once("file2.php");

$c = "three";

<?php

require_once("file3.php");

$d = "four";

echo "A is $a";
                                                                                                                                                                                                                                             [779] Wed 10.Feb.2016 13:30:51
[admin@forms][/tmp] php file4.php
A is one

[Paul_help_]

Thanks.

But in order for me to get the answer i need (so i can understand things better), i just need to refer back to my most recent post (above) where i illustrate things for question 'number 2'.

Are you telling me that, in my example (above), where I have:

file4.php
require_once( file3.php )

...... this should be enough to access the contents of 'file 1'?

[Weedpacket]

I just ran a test where a chain of a thousand files [font=monospace]require_once[/font]d each other, and information in the first was still available in the last.

[dalecosp]

Paul help!;11053583 wrote:

...... this should be enough to access the contents of 'file 1'?

No, you also need file3.php to require file2.php, and file2.php to require file1.php, and THEN file4.php has access to the content of file1.php.

[dalecosp]

Weedpacket;11053585 wrote:

I just ran a test where a chain of a thousand files [font=monospace]require_once[/font]d each other, and information in the first was still available in the last.

You're too dedicated!

(Actually, too smart ... I'm not sure at this moment just how I'd automate such a process 😉 )

[Derokorian]

dalecosp;11053595 wrote:

(Actually, too smart ... I'm not sure at this moment just how I'd automate such a process 😉 )

<?php

file_put_contents('file0.php', '<?php $var = "__SUCCESS__\n"; ');

assert_options(ASSERT_CALLBACK, function(...$args) {
    echo "FAILED running tests\n";
    exit(1);
});

$count = intval($argv[1] ?? 10);
for ($i=1; $i<=$count; $i++) {
    file_put_contents('file'. $i .'.php', '<?php require "file'. ($i-1) .'.php"; echo $var;');
    assert('"__SUCCESS__" == trim(exec("php file'. $i .'.php"))');
}

echo "Successfully confirmed that when creating $count files, the chain successfully sees the first files contents\n";

If you have xdebug installed, you will probably have problems with max_nesting_level if you run this for too many files.