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Showing posts from September, 2017

What is an earthquake?

Earthquakes with magnitude of about 2.0 or less are usually called microearthquakes; they are not commonly felt by people and are generally recorded only on local seismographs. Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On the average, one earthquake of such size occurs somewhere in the world each year. Magnitude measures the energy released at the source of the earthquake as determined from measurements on seismographs. An earthquake has one magnitude. The magnitude scale most commonly in use now is called the moment magnitude scale. Moment is a physical quantity proportional to the slip on the fault times the area of the fault surface that slips; it is related to the total energy released in the EQ. The moment magnitude p

How to change a MySQL database’s table prefix

Changing a database table prefix is easy and here’s the simple step-by-step guide! For WordPress installations, it’s essential! How to change a prefix 1. In your text editor, change database_name, old_prefix_ and new_prefix_ to the required values: SET @database = "database_name"; SET @old_prefix = "old_prefix_"; SET @new_prefix = "new_prefix_"; SELECT concat( "RENAME TABLE ", TABLE_NAME, " TO ", replace(TABLE_NAME, @old_prefix, @new_prefix), ';' ) AS "SQL"  FROM information_schema.TABLES WHERE TABLE_SCHEMA = @database; 2. Run the query in cPanel or PHPMyAdmin on your WordPress database 3. The output will be a series of SQL queries that will rename the tables for you 4. Run the output 5. Done!   How to add a prefix    If your database doesn’t have a prefix at all, follow the steps above but use the below query that’s been slightly modified fo

Selecting COUNT from MySQL table by first letter of a column

Method 1: SELECT count(*) total,     SUM(case when trim(last_name) like 'a%' then 1 else 0 end) A,     SUM(case when trim(last_name) like 'b%' then 1 else 0 end) B,     SUM(case when trim(last_name) like 'c%' then 1 else 0 end) C,     SUM(case when trim(last_name) like 'd%' then 1 else 0 end) D,     SUM(case when trim(last_name) like 'e%' then 1 else 0 end) E,     SUM(case when trim(last_name) like 'f%' then 1 else 0 end) F,     SUM(case when trim(last_name) like 'g%' then 1 else 0 end) G,     SUM(case when trim(last_name) like 'h%' then 1 else 0 end) H,     SUM(case when trim(last_name) like 'i%' then 1 else 0 end) I,     SUM(case when trim(last_name) like 'j%' then 1 else 0 end) J,     SUM(case when trim(last_name) like 'k%' then 1 else 0 end) K,     SUM(case when trim(last_name) like 'l%' then 1 else 0 end) L,     SUM(case when trim(last_name) like 'm%' then 1 e

Mysql regexp to allow numbers and '+'

First, use  NOT REGEXP  instead of  !=1 . To allow  +  at the start optionally, use  ^\\+? . Since  +  is a special character in regular expressions, it must be escaped with a backslash (which must be escaped with another backslash). You then need one or more digits ( [0-9]+ ), up to the end of the string  $ . $query="UPDATE table SET phone='NULL' WHERE phone NOT REGEXP '^\+?[0-9]+$'"; This will match anything that doesn't begin optionally with  + , followed by digits only. If you also need to permit hyphens and dots in the phone number, add them into the  []  character class: '^\\+?[0-9.-]+$'

Document Expired or Webpage has expired on back button

If you have a dinamic website and want to allow your visitors to use the back button after they sent a form with the post method, the best combination I found was: <?php header("Expires: Sat, 01 Jan 2000 00:00:00 GMT"); header("Last-Modified: ".gmdate("D, d M Y H:i:s")." GMT"); header("Cache-Control: post-check=0, pre-check=0",false); session_cache_limiter("must-revalidate"); // and after you start the sessionsession_start(); ?> I try some combinations using header("Cache-Control: no-cache, must-revalidate"), but when clicking the back button, the last changes in the form back to their previous states. The combination above works fine with IE 6.x. I didn't test this with other browsers. When I try something like session_cache_limiter("nocache, must-revalidate") it doesn't work. The page only updates when I used the browser's refresh button. In dynamic web sites this is not g

CodeIgniter Top 50 Interview Questions and Answers

1) Explain what is CodeIgniter? Codeigniter is an open source framework for web application. It is used to develop websites on PHP. It is loosely based on MVC pattern, and it is easy to use compare to other PHP framework. 2) Explain what are hooks in CodeIgniter? Codeigniter’s hooks feature provides a way to change the inner working of the framework without hacking the core files. In other word, hooks allow you to execute a script with a particular path within the Codeigniter. Usually, it is defined in application/config/hooks.php file. The hooks feature can be globally enabled/disabled by setting the following item in the application/config/config.php file: $config[‘enablehooks’] = TRUE; 3) Explain how you will load or add a model in CodeIgniter? Within your controller functions, models will typically be loaded; you will use the function $this->load->model (‘Model_Name’); 4) Explain what helpers in CodeIgniter are and how you can load a helper file? In CodeIgniter,

How to change the session timeout in PHP

Session timeout is a notion that has to be implemented in code if you want strict guarantees; that's the only way you can be absolutely certain that no session ever will survive after X minutes of inactivity. If relaxing this requirement a little is acceptable and you are fine with placing a lower bound instead of a strict limit to the duration, you can do so easily and without writing custom logic. Convenience in relaxed environments: how and why If your sessions are implemented with cookies (which they probably are), and if the clients are not malicious, you can set an upper bound on the session duration by tweaking certain parameters. If you are using PHP's default session handling with cookies, setting session.gc_maxlifetime along with session_set_cookie_params should work for you like this: // server should keep session data for AT LEAST 1 hour  ini_set('session.gc_maxlifetime', 3600);   // each client should remember their session id for EXACTLY 1 hour