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#3208 Some Tips When It Comes To Mysql Queries

Posted by Antonio Conte on 20 August 2011 - 11:19 PM

1. Always name your tables the same way:
There are best practice rules for naming tables. They should always be lowercase, split by underscore ( _ ) and named in plural. If you need to build tables for several purposes, (forums, shops, fruits) prefix them so the appear next to each other.


2. Use normalization rules(!!!) when creating a structure for tables
Larry explains the different forms of normalization very good in this book. Read it thoroughly, UNDERSTAND it, and plan your tables well. The rules are really not that hard to understand, and will allow you to cross-reference tables in an easy way later on. It will make you understand how the data you are using are working. It will make your systems a lot easier to build on and to introduce new features. I promise you, THIS is how you become a wizard when it comes to working with data in several tables.

3. Use white space(!) and use UPPERCASE for mysql functions (See tip #4!)
When your queries becomes increasingly more complex, you should really follow these tips. To demonstrate, I will give you two versions of the exact same code:

CREATE VIEW view_goals_per_game AS

SELECT league.season AS season,
league.id AS league_id,
league.name AS league_name,
goals.match_id AS match_id,
clubs1.name AS hometeam,
clubs2.name AS awayteam,
players.id AS player_id,
CONCAT( players.fornavn, ' ', players.etternavn ) AS player_name,
goals.goal_time AS goal_time,
games.kickoff_time AS kickoff_time

FROM abc_players_goals AS goals

INNER JOIN cnk_soccer_games AS games ON ( goals.match_id = games.id )
INNER JOIN cnk_soccer_clubs AS clubs1 ON ( games.club1_id = clubs1.id )
INNER JOIN cnk_soccer_clubs AS clubs2 ON ( games.club2_id = clubs2.id )
INNER JOIN abc_players AS players ON ( goals.player_id = players.id )
INNER JOIN cnk_soccer_league AS league ON ( league.id = games.league_id )

LIMIT 0, 1000

create view view_goals_per_game as select league.season as season, league.id as league_id, league.name as league_name, goals.match_id as match_id, clubs1.name as hometeam, clubs2.name as awayteam, players.id as player_id, concat( players.fornavn, ' ', players.etternavn ) as player_name, goals.goal_time, games.kickoff_time from abc_players_goals as goals inner join cnk_soccer_games as games on ( goals.match_id = games.id ) inner join cnk_soccer_clubs as clubs1 on ( games.club1_id = clubs1.id ) inner join cnk_soccer_clubs as clubs2 on ( games.club2_id = clubs2.id ) inner join abc_players as players on ( goals.player_id = players.id ) inner join cnk_soccer_league as league on ( league.id = games.league_id ) limit 0 , 1000

Whick one would you like to maintain? :blink:

4: Save your queries in a text editor

Yes! It sound idiotic, right? It's not. Think of this happening: You accidentally delete, modify or overwrite a query you've used a lot of time on. It will save you a lot of time, tears and the life of a few keyboards! This is also leading up tip number 5.

5. Use views instead of customizing your dataset in PHP(!)
This is a real life-saver. Think of it as including ONE central PHP file instead on chancing 10 documents every time you make a change. The views should be written to display AS MUCH information as possible. Try to think of every scenario you may want to use the data. Views are, with a few exceptions, for displaying data; hence it's name.

NOTE: After the creation of a view, you CANNOT modify it. This is why you should follow step 4.

- Views are really easy to create:
[u][i]CREATE VIEW the_name_of_the_view AS[/i][/u]
FROM table1

The query used in tip #3 is a view. It would allow you to sort by a specific league, match_id, player_id or by kickoff_time. The view is used to display statistic about the goal scorer in a football match. (soccer for americans) The table for saving goal statistic has three rows(!). Match_id, player_id and goal_time. This is good data normalization, and minimizes redundancy and make for consistent data. That means the table players_goals need to be linked with other tables that holds data about the specific match and the specific player. This is the reason for create a view.

Don't see the point of this?
There really is one - I promise! By writing a view that is general and display a lot of data, I can write SIMPLE queries to get different results:

1. Last five goal scorers with name of both teams, player name and goal time
SELECT hometeam, awayteam, player_name, goal_time
FROM view_goals_per_game 
ORDER BY kickoff_time DESC

2. Display players with most goals in descending order
SELECT player_name, COUNT(*) as goals
FROM view_goals_per_game
GROUP BY player_id

3. Display all goals by a specific player
 SELECT hometeam, awayteam, player_name, goal_time
FROM view_goals_per_game
WHERE player_id = 10
ORDER BY kickoff_time DESC

4. Find all goals in a specific match
SELECT hometeam, awayteam, player_name, goal_time
FROM view_goals_per_game
WHERE match_id = 837

Does it start to make some sense? Instead of repeating and modifying the same hard-to-grasp code over and over again (see tip #3), use a view to make your life simpler. :)

Hope this has helped someone. I have been thinking about writing a lot of different tips when it comes to MySQL. I've been thinking about writing a guide to joins for example. I really don't know if this interests someone or not.

Hoping others will also share tips and experiences when it comes to MySQL. :)
  • 4

#14402 Really Disturbing

Posted by margaux on 1 May 2013 - 4:56 PM

Hey xto, I'm going to try to say this in the nicest way possible -  You're in danger of trying people's patience not because you ask questions, we like questions, but because you ask questions in a way that doesn't provide the information needed to try to answer them.


1. please read the forum guidelines - Look for the little grey text bottom right of most pages, labelled Guidelines

2. please post only RELEVANT code and error messages within code tags. We don't need to see the entire output from your error message. It's actually distracting. Use code tags which are on the edit bar and they look like <>

3. post the relevant CODE, you keep posting the error message but not any code.

4. You should start a new thread for each new question. One reason for doing so is that other people with the same question can search and find your thread. If your question is part of another thread, it won't be found and won't help others.

5. You're asking questions that you should be able to solve 1 because the level of  experience for this book expects you know some basic debugging strategies and 2. with a little bit of online searching you would get some pointers as to where to look for the cause of your error.


I really shouldn't answer your question given the above but ...


somewhere in your code you are referencing an array value using 'sale_price' as the index, which doesn't exist. I'm going to hazard a guess that you have a line that includes $row['sale_price']. From the error dump you posted, you will see there is no index 'sale_price' but there is one named 'price'. Given what info you've provided that's all I can help with. If this doesn't help solve the problem, start a new thread and post the code that is causing the error :)

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#6039 Securing Video

Posted by Paul Swanson on 17 February 2012 - 5:40 PM

In addition to Rob's suggestion, you could use a .htaccess file in the directory housing the video to protect it from browsing. This will prevent any browser from accessing the directory (but PHP will still be able to access it):

# disable directory browsing
Options All -Indexes

# prevent folder listing
IndexIgnore *

# prevent access to any file
<FilesMatch "^.*$">
 Order Allow,Deny
 Deny from all

  • 3

#20294 Php/mysql Error Message?

Posted by Emilie on 19 August 2014 - 7:53 AM



MySQL doesn't 'know' the variables you created with PHP. In order to test your query, you need to replace the variables with their values.


I hope this helps,



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#15289 Use Data Type Enum For Form Drop-Down Options

Posted by margaux on 2 July 2013 - 5:02 PM

Glad I could provide a little help. When I'm struggling with some code, I use var_dump and print_r to see what is being returned. Then I know how to manipulate the data.

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#14154 Multiple Mysql_Fetch_Array That Drives Me Nuts

Posted by HartleySan on 18 April 2013 - 3:12 PM

Hmmm... I'm not entirely sure what you're going for, but I'm definitely seeing some serious inefficiencies. While I don't know the sizes of your tables (i.e., how many records each one contains), you seem to be grabbing everything from the purchases table, and within that while loop, you are then grabbing everything from the other two tables where a certain value equals a certain value in the purchases table.
Also, a lot of the math you're doing (for example, adding up values for the amount of a given order) and formatting of the date can be done on the DB side, which can further speed things up.
In general, I think your goal should be to format all your data exactly the way you want to print it out to the screen by using one query. That may not be possible, and I'm not entirely sure what you want, but I'm thinking that we *may* be able to get everything you want in one query. I will attempt to do so below, but I can't guarantee that it'll work.
To start with, I'm trying really hard to figure out what exactly you're going for, but it's a bit abstract with the variables you're using. I'm not sure if you're using those variables on purpose to disguise your code for this thread, or if you're really using those variables in your code, but either way, I would definitely recommend using more logical variable names.
Anyway, here's my interpretation of your code:
You're printing out a table of purchase orders. The first column is the row number (which you do not seem to be properly incrementing within the outer while loop). The second column is the ID of a purchase order that a customer has made. The third column is the name of the customer (and it looks like you're storing their first and last name in one column in the customers table, which I would recommend against). The fourth column is the date and time of the purchase. The fifth column is the total amount of the purchase order formatted in dollars and cents. Lastly, I'm not sure what the last two columns are, but they aren't coming from DB data, so I'll ignore those for now.
Assuming my interpretation above is correct, I think you need to do an inner join across three tables with the purchases table being the main table. Also, I think you need to group your purchases together by the purchase ID, so that you can use an aggregate function to add up the price of the individual items within each specific order.
Does that make sense?
Anyway, here's the query that I'm *thinking* will work (but I can't guarantee that it does or that it's what you want):
SELECT c.cust_id, c.name AS cust_name, p.po_id AS order_num, p.cust_id, DATE_FORMAT(p.timestamp, '%m %d, %Y') AS date, o.po_id, SUM(o.delivered * o.srp) AS amount
FROM customers AS c, purchases AS p, po_content AS o
WHERE c.cust_id = p.cust_id AND p.po_id = o.po_id
GROUP BY o.po_id
ORDER BY p.timestamp ASC
LIMIT $start $display;
A few notes about the query:
1) For your query, a join is essential. Specifically, two inner joins on the purchases table is what you need. Joins are tricky at first, but they're essential for most DBs, so I'd recommend studying up on them.
2) Only select the columns you need. Using SELECT * for three separate queries is getting you a lot of data you don't need, and is very inefficient.
3) Use aliases (e.g., "AS c", "AS p", etc.) on the tables to make typing out the query shorter and easier. Also, aliases are essential for being able to easily reference the results of aggregate functions, formatted, dates, etc.
4) Format the timestamp on the SQL side using the DATE_FORMAT function. It's faster and easier. Also, give the formatted date an alias to make it easier to access on the PHP side. Here's more info on the DATE_FORMAT function:
5) I'd calculate the total amount of each order on the SQL side. To do so, you need to use the SUM aggregate function, and also use the GROUP BY clause to group your results together by order number so that you are adding up the correct grouping of items. Also, I'd assign an alias to the result of the SUM function.
6) The "ASC" part of the query is not necessary, since that's the default ordering. I left it anyway to avoid any further confusion.
7) I used "o" as the alias of the po_content table, as it seems like a table of orders to me.
That will hopefully handle the query side of things.
Unfortunately, I think there are some other issues with your code as well:
1) You're not incrementing $rownum in the while loop.
2) You're assigning your $bgcolor value to the entire table, not individual table rows. Also, I'm pretty sure the resulting HTML will be syntactically invalid and not work.
3) You're creating a new table each time through the while loop.
4) You're putting a div within a td for the total, which I wouldn't do.
Point being, without sounding too harsh, I think your code has some serious issues and needs some re-working. I get the feeling that you might be getting a bit too ambitious about your personal project without first understanding all the basics you need.
I don't mean to say that you shouldn't be ambitious, but I think you should probably go back to the book for a bit and bone up on queries with joins, HTML and PHP syntax, as well as think more about the logic of your while loop and the type of HTML that it is creating.
Anyway, below, I'm going to present the PHP I would use for your situation. Again, please keep in mind that I'm doing my best to piece together exactly what you want (and I'm not entirely sure), so I could be way off on this.
// I'm assuming that $agent and $encoder are already defined above.
$row_num = 1;
$total = 0;
$bg_color = '#FFF';
$q = "SELECT c.cust_id, c.name AS cust_name, p.po_id AS order_num, p.cust_id, DATE_FORMAT(p.timestamp, '%m %d, %Y') AS date, o.po_id, SUM(o.delivered * o.srp) AS amount FROM customers AS c, purchases AS p, po_content AS o WHERE c.cust_id = p.cust_id AND p.po_id = o.po_id GROUP BY o.po_id ORDER BY p.timestamp ASC LIMIT $start $display;";
// I'm assuming that $start and $display are already defined above.
$r = mysqli_query($dbc, $r);
// I am assuming that $dbc is already defined above. You also seem to have omitted this argument in your code.
echo '<table class="order_details">';
// I'd use CSS to properly format the table instead of the inline attributes you're using.
// As such, I have assigned a class to the table for that exact reason.
// Also, your table doesn't have any headers, but you may want to add them along with thead, th, tbody, and tfoot tags.
while ($row = mysqli_fetch_array($r, MYSQLI_ASSOC)) {
  echo '<tr style="background-color: ' . $bg_color . ';">
  <td>' . $row_num . '</td>
  <td>' . $row['order_num'] . '</td>
  <td>' . $row['cust_name'] . '</td>
  <td>' . $row['date'] . '</td>
  <td>' . number_format($row['amount'], 2) . '</td>
  <td>' . $agent . '</td>
  <td>' . $encoder . '</td>
  $row_num++; // Don't forget to increment this.
  $total += $row['amount']; // This is the summation of the unformatted amounts, which could cause issues.
  $bg_color = ($row_num % 2 === 0) ? '#F3F3F3' : '#FFF'; // Ternary operation for brevity
echo '<tr style="background-color: ' . $bg_color . ';">
<td colspan="4" class="total_row">Total</td>
<td>' . number_format($total, 2) . '</td>
// Formatted to line up with the amount column.
// Also, note that I handled the total the same way you did, but if you calculate the total on the
// unformatted amount values, then you may get a discrepancy in which the amounts don't add up to the total.
// Also, again, I'd use CSS (not inline HTML) to align "Total" to the right.
// Lastly, you may want to put the total in a tfoot element.
Well, I think that's about it.
After all this writing, I really hope that I got close to what you wanted, and that this post is of some use.
Please let me know.

  • 3

#13394 Pls Help Need Urgent Help. The .Inc Extension. Chapter 11

Posted by margaux on 11 March 2013 - 4:45 AM

It's difficult to debug when the code is presented in this way. Please would you use code tags.


At first look, no error immediately jumps out. Which line is line 46? Look at that line and the few lines before it.


Probably not causing this error but it looks like you may have a typo on the tablename in the SELECT statement - users instead of usera?

  • 3

#11924 Very Basic: Headers Vs Cookies

Posted by HartleySan on 27 December 2012 - 8:38 PM

The order doesn't matter. In fact, you can perform any number of PHP operations before setting headers so long as you don't actually output any HTML before you set a header.
  • 3

#11512 Exception Handling For Flow Control?

Posted by Antonio Conte on 6 December 2012 - 6:46 PM

It depends. More often than not, application breaking errors should throw exception. As an example, an invalid date, improper email addresses or bad zip codes could benefit from throwing exceptions. The reason for that is data integrity. A class/function could very well be dependent of having valid data on a special format to be able to perform actions/calculations of it.

You'll often see people defining their own exceptions like so. In this example we have a example class for sending email. It's no point sending an email to "111lol!", so then it's good practice to throw an exception. (

class Email
public function send( $email )
    if (! filter_var($email, FILTER_VALIDATE_EMAIL))
	    throw new InvalidEmailAddressException("Invalid email adress provided.");

// Email exception
class InvalidEmailAddressException extends Exception
    public function __construct($message) { parent::__construct($message); }

Hope that gives you a general idea. Short answer would be this: for "checking values", use return values. User::add() could return true/false on how the adding went. For invalid values that could break classes/methods, throw exceptions.
  • 3

#11339 Ch. 11 Using Unlink() With A Reset Button Possible?

Posted by Antonio Conte on 27 November 2012 - 10:43 PM

This can absolutely be done via GET. What you would do is using IDs as the get value. Save the filenames to an array on the form ID => "name". You then build links the same way, but with ?remove=$ID. You cast $_GET['id'] to an integer, find the filename in array by using the ID, build a full path where you add the filename, then use unlink() to delete the file.

An easy way to do this would be something like:

$handle = ""; // open file

$file_array = array(); // The file names

while ( ($file = readdir($handle)) !== false )
    if ($entry != "." && $entry != "..")
	   $file_array[] = $file;
    } // Read files to array

// Simple delete
if ( ! empty($_GET) )
    $upload_dir = "uploadsDirectoryHere/"; // Upload dir
    $file_id = (int) $_GET['delete']; // File_array ID

    // Make sure file is found
    if ( array_key_exists($file_id, $file_array) )
		 $delete_file = $upload_dir . $file_array[$file_id];

		 // Make sure file exists
		 if ( file_exists($delete_file) )
			  unset(file_array[$file_id]); // Remove from file array
			  unlink($delete_file); // Actually delete file here

// Print out file names and links for deleting them
foreach ( $file_array as $id => $filename )
    echo $filename . '<a href="page.php?delete='.$id.'">Delete file</a>;

Not tested, but that should be the basic idea. Sorry about errors/etc. Beginning to get tired here.
  • 3

#10740 Paypal Integration Confusion

Posted by MrJames on 29 October 2012 - 7:14 AM


Try the following as an example:

<input type="hidden" name="amount" value=" ' . $productPrice . ' ">

  • 3

#10649 Advanced Question - What Is Happening In This For In Loop?

Posted by HartleySan on 24 October 2012 - 2:53 AM

When you ask for more "explicit" code to accomplish the same thing, I assume that you're really asking, "What's a simple way to accomplish the same thing?"

I'm not sure if there's a simpler way, as "simpler" code might actually be more confusing for a JS guru, but for demonstration purposes, I have put together some sample code that achieves the same thing without the use of closures (at least, not in the sense that you're thinking about) and without the use of the map method.

Keep in mind that my code is super simplistic, and I wouldn't actually recommend ever doing things this way, but for demonstration purposes, I think it serves its purpose well.

<!DOCTYPE html>

<html lang="en">


    <meta charset="UTF-8">

    <title>Chaining alternative</title>



    <a href="#" id="link1">Link 1</a>

    <a href="#" id="link2">Link 2</a>

    <a href="#" id="link3">Link 3</a>


      // this in these two functions is equal to the out array in function X.

      function color(x) {

        for (var i = 0; i < this.length; i++) {

          this[i].style.color = x;


        return this;


      function size(x) {

        for (var i = 0; i < this.length; i++) {

          this[i].style.fontSize = x;


        return this;


      function X(css) {

        var out = [];

        // For this simplified example, I'm assuming that css is always a tag name, not an ID.
        var tags = document.getElementsByTagName(css);

        for (var i = 0; i < tags.length; i++) {



        out['color'] = color;

        out['size'] = size;

        return out;






Does that help clarify things at all?

I know that that one guy's code on the other site is very difficult, so don't feel bad if it doesn't all click right away. He has a ton of complex code (and sometimes JS-specific idiosyncrasies) all stuck together.

To reply to your three points of interest:

1) Yes, scope in JS is very interesting. The thing about JS is that functions are lexically scoped, meaning that they contain the scope in which they're defined, not in which they are called. This is different from C, for example.

2) Yes, I agree that the way the length property is calculated in JS is interesting, but that's just the way it's defined in the ECMA specs (for better or worse). To give some more explanation, if an array contains only associative indexes, since that's akin to an object (not an array) in JS, the length will be 0. Another interesting caveat is that if, for example, you have an array with only 1 element, but the index of that element is 5, then the length will be reported as 6 (as per what I said in my previous post (i.e., 5 + 1)).

3) Closures are basically used as a tricky way to freeze a variable's state in time. For example, you may have a constantly changing global variable, but if you want to retain the value of that variable at one specific time, then you need to use a closure. Remember that every time a function is called, a closure is created (just usually not a closure in the sense that's commonly talked about). This happens because whenever a function is called, all the variables passed to that function are frozen in the state that they are in when the function was called. It's prudent to remember that this is NOT the case with function references/function definitions; only function calls. Anyway, for the m example, if you just remember that m is equal a specific instance of meths[meth] each time through the for-in loop, then you should be fine.

Hope that helps (and by all means, fire back another comment if it doesn't).
  • 3

#20055 I'm Having Trouble With Sorting Query Results In Chapter 5... Plz Help!

Posted by Emilie on 30 July 2014 - 1:07 PM



What is "wrong", according to you?


The registration date is the same for all users because you entered all of them at one go into the database, and therefore the timestamp corresponding to NOW() is the same for everyone. Because of that, ordering the results by registration_date DESC has no real meaning.


I hope this helps,



  • 3