This column contains additional information about how MySql resolved the query. There is a line in the manual which states: If you want to make your queries as fast as possible, look out for Extra values of Using filesort and Using temporary. Let’s examine why
SQL EXPLAIN: The “filtered” column
The filtered column shows an estimated percentage of rows that will be filtered by the table WHERE clause. It’s typically only shown during the EXPLAIN EXTENDED command.
SQL EXPLAIN: The “ref” column
The “ref” column shows which columns or constants are compared to the index named in the “key” column to select rows from the table. This comes right from the manual, but I have noticed that when the value is const,
SQL EXPLAIN: Index-related columns
These relate to the usage of indexes: possible_keys Which indexes were considered? key Which indexes did the optimizer choose? key_len How many bytes of the index will be used?
SQL EXPLAIN: The “type” column
The “type” column indicates how MySQL will access rows From worse to better: ALL index range ref eq_ref const system NULL
A faster alternative to correlated sub-queries
I recently had to rewrite a query that was running very slowly. It was taking over 30 seconds. Upon analyzing it, I saw that it had 2 correlated sub-queries in it, and each was doing a count(*). This meant that
You might not need jQuery…
I just found a video that talks about how jQuery is no longer needed in 2018. I found it interesting, and thought I’d save it and some related pages here for future reference. http://microjs.com/#ajax https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch https://caniuse.com http://youmightnotneedjquery.com/
Compact and Extract
Compact takes individual variables, and packs them into an associative array. Extract does the opposite. <?php // example code // Set 2 variables $var1 = “one”; $var2 = “two”; // Create associative array $arr = compact(‘var1′,’var2’); // Show results var_dump($arr);
Splat!
While looking through the Query Builder class in the Laravel source code today, I came across something I hadn’t seen before in PHP: $query->{$method}(…array_values($value)); I had no idea what the three dots meant, so I went looking for it. Turns
Understanding Octal
Why would we need to understand Octal? The most relevant reason I can come up with right now is that looking back at some of the interview question challenges I’ve posted, there is one that deals with an Octal number.
foreach vs array_filter
The problem: Given an array of numbers, create a new array containing only the odd numbers from the original. $original_array = [1,2,3,4,5,6,7,8,9,10]; There are two ways you can approach this problem. Let’s look at a foreach loop first: $original_array =
Factor Finder
// Number to factor $num = 60; // Loop from the number to factor down to 1 for($i=$num; $i>=1; $i–){ // If it divides evenly if($num % $i === 0 ){ // Output result of division, which is a factor
chmod
chmod is short for change mode. It is the linux command used to change file permissions. The basic format of the command is like this: chmod options permissions filename There are a number of options, but one of the more
Changing the color of the first word
The question/problem is: Write a PHP script, which changes the color of the first character of a word. This challenge tests your knowledge of preg_replace, and regular expressions. $text = ‘PHP Tutorial’; $text = preg_replace(‘/(\b[a-z])/i’,'<span style=”color: red;”>\1′,$text); echo $text; ?>
SQL sub query challenge
Goal: Write a query which will get the first and last name from the customer table, and the total amount of all that customer’s orders. SELECT first,last FROM customers C This will get all the customers.Next we need to write
Reference challenge
This one tests your knowledge of how reference variables work: $a = ‘P’; $b = &$a; $b = “PH$b”; What will $a and $b be after these three lines of code run? First, $a is set to ‘P’. Then, $b
Base class or Interface?
When making the decision to use a base class or interface, it may help to think of the implementation. If all the implementations are going to be similar, then you might want to group them under a base class. But
preg_match problem
Given: $a = “4|6|3|5|x|2|”; Write code that will output: “2|3|4|5|6” It could be done the long way round, by turning the string into an array, looping over each element, testing each item to see if it’s a number, and placing
MySql Limit
SELECT c.first_name,c.last_name, o.order_total FROM customers c LEFT OUTER JOIN orders o ON c.id = o.cust_id WHERE o.order_total > 100.0 I was once asked to write a query similar to this. The goal was to select all customers who had placed
Array Sorting
I came across this problem recently: How would you sort an array of strings to their natural case-insensitive order, while maintaining their original index association? array( ‘0’ => ‘z1’, ‘1’ => ‘Z10’, ‘2’ => ‘z12’, ‘3’ => ‘Z2’, ‘4’ =>