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How to Handle Duplicate Records by Deleting and Leaving Only One Record from Each Duplicate Records in MySQL Database

Masino Sinaga — Fri, 15 Jul 2011 15:56:45 +0000

Have you ever got difficulty when handling the duplicate records in a table in MySQL database, where you want to delete the records and pretty leaves one record from each duplicate records? This usually happens in the table who did not have the primary key, so that it can cause to store the duplicate records. The duplicate records are usually obtained from the data import process that was done repeatedly. Well, the following trick you can use to handle such cases. Quite easy and a little bit outsmart. The first step, you must copy the table structure that stores the duplicate records to another table name (copy table structure only, not including records). The second step, simply copy only one or distinct record from each duplicate records using a single MySQL statement to the copied/destination table. Lastly, the third step, check the results in the destination table. If everything goes smoothly, then delete the original table, and rename back the copied/destination table to the original table name. Curious?

For example, you have a table named table1 which has the structure like this:

mysql> DESCRIBE `table1`;
+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| code        | char(2)     | YES  |     |         |       |
| description | varchar(50) | YES  |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+

and it has the duplicate records as following:

mysql> select * from table1;
+------+-------------+
| code | description |
+------+-------------+
| 1    | One         |
| 1    | One         |
| 2    | Two         |
| 2    | Two         |
| 3    | Three       |
| 3    | Three       |
| 3    | Three       |
| 4    | Four        |
| 4    | Four        |
| 4    | Four        |
| 4    | Four        |
| 5    | Five        |
| 5    | Five        |
| 5    | Five        |
| 5    | Five        |
| 5    | Five        |
+------+-------------+

Let’s say, you want to delete and leave only one record from each the duplicate records. So the results become like this:

+------+-------------+
| code | description |
+------+-------------+
| 1    | One         |
| 2    | Two         |
| 3    | Three       |
| 4    | Four        |
| 5    | Five        |
+------+-------------+

So, in order to get that results, copy only the table structure of table1 to (for example) table1_copy using the following SQL statement:

mysql> CREATE TABLE `table1_copy` LIKE `table1`;

Afterwards, copy or insert only one record of the duplicate records from table1 into the table1_copy using the following SQL statement:

INSERT INTO table1_copy
SELECT DISTINCT * FROM table1;

Voila… here is the result:

mysql> SELECT * FROM table1_copy;
+------+-------------+
| code | description |
+------+-------------+
| 1    | One         |
| 2    | Two         |
| 3    | Three       |
| 4    | Four        |
| 5    | Five        |
+------+-------------+

Ups, don’t forget to remove the table1 table (assuming all the steps above goes smoothly):

DROP TABLE IF EXISTS `table1`;

and then rename the destination table to the original one:

RENAME TABLE `table1_copy` TO `table1`;

It’s very easy, isn’t?

How to Replace the Certain Character in a MySQL Table

Masino Sinaga — Mon, 09 Aug 2010 07:08:08 +0000

Have you ever encountered the strange behavior while you were deleting the certain records from a table in MySQL database using an application you build, which those records cannot be deleted? Well, I have! Today, I encountered this problem. This is so weird, since I have never faced this situation before. Well, after doing some investigations, this problem obviously caused by one of the primary key fields contains the comma (,) character. Why I am sure about this, because when I replace the comma character for one record, then I re-try to delete that record from that application, voila…. that record gets successfully deleted. But the main problem is not stop until that. The next question is: How then can I replace all comma characters from the rest of the other records immediately? Just for your information, there are thousand records that contain the comma character. It is impossible to update all the records one by one, even as a matter of fact, you can create a little program/tool in order to implement it using loop method throught the recordset? Well, here is the quick-solution to overcome it.

MySQL has provided the great UPDATE SQL syntax for this. You can use this SQL (for instance, I want to replace the comma character inside the tablename table with the minus character that located in a field named thefield):

UPDATE tablename SET `thefield` = REPLACE(`thefield`, ',', '-');

Isn’t easy, huh?

How to Remove Product ID from URL of PrestaShop version 1.2.5

Masino Sinaga — Tue, 04 May 2010 03:38:46 +0000

Have you ever wanted to remove the product id from the URL of your PrestaShop? For instance, by default, PrestaShop uses this URL to display the certain product named ipod-touch: /7-ipod-touch.html instead of /ipod-touch.html. Well, here is the solution how you can make it comes true. I have successfully implemented it into PrestaShop version 1.2.5. Please note that before you implement this modification, make sure you have already implemented the similar modification that will remove category id from the URL.

Make sure that you have already had the .htaccess file in your PrestaShop’s root directory, which has the content like the following:

# .htaccess automaticaly generated by PrestaShop e-commerce open-source solution
# http://www.prestashop.com - http://www.prestashop.com/forums
 
# URL rewriting module activation
RewriteEngine on
 
# URL rewriting rules
RewriteRule ^([a-z0-9]+)\-([a-z0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /prestashop1250/img/p/$1-$2$3.jpg [L,E]
RewriteRule ^([0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /prestashop1250/img/c/$1$2.jpg [L,E]
RewriteRule ^lang-([a-z]{2})/([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /prestashop1250/product.php?id_product=$3&isolang=$1$5 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /prestashop1250/product.php?id_product=$2&isolang=$1$4 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /prestashop1250/category.php?id_category=$2&isolang=$1 [QSA,L,E]
RewriteRule ^([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /prestashop1250/product.php?id_product=$2$4 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /prestashop1250/product.php?id_product=$1$3 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /prestashop1250/category.php?id_category=$1 [QSA,L,E]
RewriteRule ^content/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /prestashop1250/cms.php?id_cms=$1 [QSA,L,E]
RewriteRule ^([0-9]+)__([a-zA-Z0-9-]*)(.*)$ /prestashop1250/supplier.php?id_supplier=$1$3 [QSA,L,E]
RewriteRule ^([0-9]+)_([a-zA-Z0-9-]*)(.*)$ /prestashop1250/manufacturer.php?id_manufacturer=$1$3 [QSA,L,E]
RewriteRule ^lang-([a-z]{2})/(.*)$ /prestashop1250/$2?isolang=$1 [QSA,L,E]
 
# Catch 404 errors
ErrorDocument 404 /prestashop1250/404.php
 
# Remove Category ID from URL. You have to modify also the /classes/Link.php file! Modified by Masino Sinaga, May 3, 2010
RewriteRule ^accessories-ipod$ /prestashop1250/category.php?id_category=3 [QSA,L,E]
RewriteRule ^music-ipods$ /prestashop1250/category.php?id_category=2 [QSA,L,E]
RewriteRule ^laptops$ /prestashop1250/category.php?id_category=1 [QSA,L,E]

That .htaccess file is generated from the link I mentioned above about. You can generate this .htaccess file from admin panel at Tools tab, then choose Generators sub-tab, and follow the instructions carefully there. In this example above, I use prestashop1250 for the domain name. Please adjust it with yours.

Add this following code after the last line of that code above:

# Remove Product ID from URL. You have to modify also the /classes/Link.php file! Modified by Masino Sinaga, May 4, 2010
RewriteRule ^music-ipods/ipod-nano\.html(.*)$ product.php?id_product=1$1 [QSA,L,E]
RewriteRule ^music-ipods/ipod-shuffle\.html(.*)$ product.php?id_product=2$1 [QSA,L,E]
RewriteRule ^laptops/macbook-air\.html(.*)$ product.php?id_product=5$1 [QSA,L,E]
RewriteRule ^laptops/macbook\.html(.*)$ product.php?id_product=6$1 [QSA,L,E]
RewriteRule ^music-ipods/ipod-touch\.html(.*)$ product.php?id_product=7$1 [QSA,L,E]
RewriteRule ^accessories-ipod/housse-portefeuille-en-cuir-belkin-pour-ipod-nano-noir-chocolat\.html(.*)$ product.php?id_product=8$1 [QSA,L,E]
RewriteRule ^accessories-ipod/ecouteurs-a-isolation-sonore-shure-se210-blanc\.html(.*)$ product.php?id_product=9$1 [QSA,L,E]

It meant that we will adjust the 7 products name: ipod-nano, ipod-shuffle, macbook-air, macbook, ipod-touch, housse-portefeuille-en-cuir-belkin-pour-ipod-nano-noir-chocolat, and ecouteurs-a-isolation-sonore-shure-se210-blanc. In other words, if you have more than 7 products above, you have to define or add your own product one by one into the .htaccess file.

Open your /classes/Link.php file, find this code:

	public function getProductLink($id_product, $alias = NULL, $category = NULL, $ean13 = NULL)
	{
	 	if (!isset($this->allow)) $this->allow = 0;
		if (is_object($id_product))
			return ($this->allow == 1)?(_PS_BASE_URL_.__PS_BASE_URI__.(($id_product->category != 'home' AND !empty($id_product->category)) ? $id_product->category .'/' : '').intval($id_product->id).'-'.$id_product->link_rewrite.($id_product->ean13 ? '-'.$id_product->ean13 : '').'.html') : 
			(_PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product->id));
		elseif ($alias)
			return ($this->allow == 1)?(_PS_BASE_URL_.__PS_BASE_URI__.(($category AND $category != 'home') ? ($category.'/') : '').intval($id_product).'-'.$alias.($ean13 ? '-'.$ean13 : '').'.html') : 
			(_PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product));
		else
			return _PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product);
	}

then replace with this following code:

	public function getProductLink($id_product, $alias = NULL, $category = NULL, $ean13 = NULL)
	{
	 	if (!isset($this->allow)) $this->allow = 0;
		if (is_object($id_product))
			return ($this->allow == 1)?(_PS_BASE_URL_.__PS_BASE_URI__.(($id_product->category != 'home' AND !empty($id_product->category)) ? $id_product->category .'/' : '')./*intval($id_product->id).'-'.*/$id_product->link_rewrite.($id_product->ean13 ? '-'.$id_product->ean13 : '').'.html') : 
			(_PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product->id));
		elseif ($alias)
			return ($this->allow == 1)?(_PS_BASE_URL_.__PS_BASE_URI__.(($category AND $category != 'home') ? ($category.'/') : '')./*intval($id_product).'-'.*/$alias.($ean13 ? '-'.$ean13 : '').'.html') : 
			(_PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product));
		else
			return _PS_BASE_URL_.__PS_BASE_URI__.'product.php?id_product='.intval($id_product);
	}

Now you should have the URL without the category and product id in it.