BRADINO » MySQL

MySQL Query Cache

BRADINO — Tue, 21 Jul 2009 00:20:28 +0000

According to MySQL.com the query cache stores the text of a SELECT statement together with the corresponding result that was sent to the client. If an identical statement is received later, the server retrieves the results from the query cache rather than parsing and executing the statement again. The query cache is shared among sessions, so a result set generated by one client can be sent in response to the same query issued by another client.

Purely hypothetical example:

SELECT `name` FROM `beers` WHERE `favorite` = true

To force the database NOT to give you a cached result simply add SQL_NO_CACHE to the query:

SELECT SQL_NO_CACHE `name` FROM `beers` WHERE `favorite` = true

Count Email Address Domains

BRADINO — Wed, 15 Jul 2009 01:03:16 +0000

A quick tidbit I came up with today to count email addresses in a mysql database table grouping them by domain. So say for example you have a large list of subscribers and you want to see the breakdown of people who use Hotmail, Yahoo, Gmail, etc.

SELECT COUNT( SUBSTRING_INDEX( `email` , '@', -1 ) ) AS `count` ,
SUBSTRING_INDEX( `email` , '@', -1 ) AS `domain`
FROM `subscribers` WHERE `email` != ''
GROUP BY `domain`
ORDER BY `count` DESC

This sql statement assumes that the table is called 'subscribers' and the column containing the email addresses is 'email'. Change these two values to match your table name and email address column name.

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Calculate Age using Date Field

BRADINO — Thu, 19 Feb 2009 00:45:08 +0000

So if you have a database table that has DOB borthdays as date fields, this is an easy way to query that table based on age parameters. The following examples assume that the date of birth date field is dob and the table name is people.

Find people who are 30 years old

SELECT DATE_FORMAT( FROM_DAYS( TO_DAYS( now( ) ) - TO_DAYS( `dob` ) ) , '%Y' ) +0 AS `age`
FROM `people` HAVING `age` = 30

Find people who are 31-42 years old

SELECT DATE_FORMAT( FROM_DAYS( TO_DAYS( now( ) ) - TO_DAYS( `dob` ) ) , '%Y' ) +0 AS `age`
FROM `people` HAVING `age`>= 31 AND `age` <= 42

Find oldest person

SELECT MAX(DATE_FORMAT( FROM_DAYS( TO_DAYS( now( ) ) - TO_DAYS( `dob` ) ) , '%Y' ) +0) AS `age`
FROM `people`

Find youngest person

SELECT MIN(DATE_FORMAT( FROM_DAYS( TO_DAYS( now( ) ) - TO_DAYS( `dob` ) ) , '%Y' ) +0) AS `age`
FROM `people`

SQL SELECT WHERE IN

BRADINO — Fri, 21 Nov 2008 18:33:03 +0000

Here is a basic sql statement where you are looking for shirts that are red, white or blue.

SELECT * FROM `shirts` WHERE `color`='red' OR `color`='white' OR `color`='blue'

Here is the same request, more efficiently constructed using IN

SELECT * FROM `shirts` WHERE `color` IN ('red','white','blue')

If you are like me and dynamically create SQL statements using PHP then you get the idea of how easy it would be to create this statement. Let's say you have an array of possible value.

$colors = array('red','white','blue');

$sql = "SELECT * FROM `shirts` WHERE `color` IN ('" . implode("','", $colors) . "')" ;

mysql select in select in where select in

Simple MySQL Database Backup

BRADINO — Wed, 01 Oct 2008 23:31:56 +0000

This is the simplest way to backup MySQL databases and tables using the mysqldump command to generate an sql file. I will also show you how to restore the database or table from the generated sql file and demonstrate a simple loop to generate a separate mysqldump of each table in a given database. This makes it really easy to restore just the table(s) that you want.

So first let's setup some global variables we will use later with some simple function calls. Database Host, database Name, Database User, Password and Path. Important to remember, Path needs to be writable by PHP and also be sure to escape and weird characters like $ in the fields.

// SETUP GLOBAL PARAMETERS

$params = array();

$params['host'] = 'localhost';

$params['database'] = 'collections';

$params['username'] = 'user007';

$params['password'] = 'asdf123';

$params['table'] = 'widgets';

$params['path'] = 'PATH/backup/';

// BACKUP A SINGLE TABLE

mysqlBackupTable($params);

// BACKUP AN ENTIRE DATABASE

mysqlBackupDatabase($params);

// RESTORE TABLE

mysqlRestoreTable($params);

// RESTORE DATABASE

mysqlRestoreDatabase($params);

// BACKUP ALL TABLES IN A DATABASE

$query = mysql_query("SHOW TABLES FROM `{$params['database']}`");

while($row = mysql_fetch_row($query)){

$params['table'] = $row[0];

mysqlBackupTable($params);

}

// FUNCTION: BACKUP MYSQL TABLE TO A FILE

function mysqlBackupTable($params){

$outfile = makeFileName($params['path'],$params['database'],$params['table']);

$cmd = "mysqldump --user={$params['username']} --password={$params['password']} {$params['database']} --tables {$params['table']}> {$outfile}";

system($cmd);

}

// FUNCTION: BACKUP MYSQL DATABASE TO A FILE

function mysqlBackupDatabase($params){

$outfile = makeFileName($params['path'],$params['database']);

$cmd = "mysqldump --user={$params['username']} --password={$params['password']} {$params['database']}> {$outfile}";

system($cmd);

}

// FUNCTION: RESTORE MYSQL TABLE

function mysqlRestoreTable($params){

$infile = makeFileName($params['path'],$params['database'],$params['table']);

$cmd = "mysql --user={$params['username']} --password={$params['password']} {$params['database']} <{$infile}";

system($cmd);

}

// FUNCTION: RESTORE MYSQL DATABASE

function mysqlRestoreDatabase($params){

$infile = makeFileName($params['path'],$params['database']);

$cmd = "mysql --user={$params['username']} --password={$params['password']} {$params['database']} <{$infile}";

system($cmd);

}

// FUNCTION: NAMING CONVENTION FOR DUMP FILES

function makeFileName($path,$database,$table=''){

return (!empty($table)) ? "{$path}{$database}@{$table}.sql" : "{$path}{$database}.sql" ;

}

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Zipcode Radius Search

BRADINO — Thu, 25 Sep 2008 20:55:42 +0000

Want to find all zipcodes and corresponding distances within a certain mile/kilometer radius from another zipcode or point? This problems require latitude and longitude coordinates to solve. Geocoding the address gives you latitude/longitude coordinates from an address. Both Yahoo and Google offer free geocoding services. I wrote a post about geocoding with a code example for both Google and Yahoo geocode services.

First you will need a database of all zipcodes and their corresponding latitude and longitude coordinates. If you are reading this post, you probably don't have this so let me help you out. Download Zipcode Database for a zip file of both an SQL data dump and CSV format. Here is the basic table structure I use in my example code:

CREATE TABLE `zipcodes` (
`zipcode` varchar(5) NOT NULL DEFAULT '',
`city` varchar(100) NOT NULL DEFAULT '',
`state` char(2) NOT NULL DEFAULT '',
`latitude` varchar(20) NOT NULL DEFAULT '',
`longitude` varchar(20) NOT NULL DEFAULT '',
KEY `zipcode` (`zipcode`),
KEY `state` (`state`)
)

So once you have the database you want to find all zipcodes within a certain mile radius of a central point. If the central point is another zipcode, simply query the database for the latitude and longitude coordinates of that zipcode. Then the code is as follows:

// ITITIAL POINT

$coords = array('latitude' => "32.8", 'longitude' => "-117.17");

//RADIUS

$radius = 30;

// SQL FOR KILOMETERS

$sql = "SELECT zipcode, ( 6371 * acos( cos( radians( {$coords['latitude']} ) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians( {$coords['longitude']} ) ) + sin( radians( {$coords['latitude']} ) ) * sin( radians( latitude ) ) ) ) AS distance FROM zipcodes HAVING distance <= {$radius} ORDER BY distance";

// SQL FOR MILES

$sql = "SELECT zipcode, ( 3959 * acos( cos( radians( {$coords['latitude']} ) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians( {$coords['longitude']} ) ) + sin( radians( {$coords['latitude']} ) ) * sin( radians( latitude ) ) ) ) AS distance FROM zipcodes HAVING distance <= {$radius} ORDER BY distance";

// OUTPUT THE ZIPCODES AND DISTANCES

$query = mysql_query($sql);

while($row = mysql_fetch_assoc($query)){

echo "{$row['zipcode']} ({$row['distance']})
\n";

}

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Dayparting on Datetime Field using Substring

BRADINO — Tue, 10 Jun 2008 17:26:16 +0000

Today I needed a quick and easy way to count the number of records for each of the 24 hours in a day for records in a mysql database that has a datetime field. I came up with the following query to solve that problem:

SELECT count( SUBSTRING( `datetime` , 12, 2 ) ) AS `num` , SUBSTRING( `datetime` , 12, 2 ) AS `hour`
FROM `table`
GROUP BY SUBSTRING( `datetime` , 12, 2 )
ORDER BY `num` DESC

mysql dayparting substring hour counts

MySQL Order By Numeric Difference

BRADINO — Fri, 09 Nov 2007 22:19:58 +0000

A nice way I found to use MySQL to order a result set by the absolute value of the numeric difference between two numbers, where one is the value in a column. I had never used SQL to subtract two numbers, let alone take the absolute value and use that to order the results. You could use something like this to show numbers that are most closely related, maybe in a zipcode application or a priority scoring application.

SELECT * FROM `table`
WHERE `something`=`whatever`
ORDER BY ABS ( 711 - `num` )

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Make CSV File from Database

BRADINO — Tue, 23 Oct 2007 19:44:23 +0000

This is the easiest way to make a CSV file from a database query and output it to the user for download. This simple code uses the PHP5 fputcsv function to correctly format an array of values into a line in a csv file. It does not use the physical file so you do not need any write permissions where you use this code, as it uses the memory buffer instead.

$output = fopen('php://temp/maxmemory:'. (5*1024*1024), 'r+');

$columns = array('Field1','Field2','Field3','Field4','Field5');

fputcsv($output, $columns);

$query = mysql_query("SELECT * FROM `table`");

while ($data = mysql_fetch_assoc($query)){

fputcsv($output, $data);
}

rewind($output);

$export = stream_get_contents($output);

fclose($output);

header('Content-type: application/octet-stream');

header('Content-Disposition: attachment; filename="export.csv"');

echo $export;

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MySQL Real Escape String

BRADINO — Fri, 19 Oct 2007 22:26:00 +0000

I always escape MySQL statement parameters from PHP using the function mysql_real_escape_string(), even after I have groomed them. One thing that I always forget is that this function will not work if you have not established a database connection. Without a database connection it returns nothing. If you have error reporting turned on, you will get a database connection error on the line that you are calling the mysql_real_escape_string() function.

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