Tuesday, July 15th, 2008
During the dark age, the simplest way to get previous row from current ID was using this query:
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SELECT field1
-
FROM tablename
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WHERE id = ($currentId - 1)
and to get next row:
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SELECT field1
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FROM tablename
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WHERE id = ($currentId + 1)
But there’s a problem. Like common data, we need to delete some rows. For example, the current ID is 14 ($currentid = 14) , and i deleted row id number 13, when i run the query to get the previous row, the result will empty. The sql cannot find ID number 13 ($currentid - 1).
How to fix it?
Again, the first simplest way i got is to loop the ID. When it cannot find the first query, it calculate again by looping it with PHP.
//the bad way..
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<?
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$ok = false;
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$prev = $currentid - 1;
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while($ok == false){
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$sql = "select * from tablename where id = $prev ";
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$data = $db->query($sql);
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if(empty($data)){
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$prev = $prev-1;
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}else{
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$ok = true;
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}
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}
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?>
This is really bad idea. It will consume more resources by continually query the database. What happen when you deleted 10 rows from current ID?
There will be 10 looping with 10 query to database. How about deleted 100 rows?? You must be insane doing this.
(more…)
Posted in coded | 4 Comments »
Thursday, July 10th, 2008
By default, you will get black background if you resize a transparent image. To fix it, you need set alpha channel imagecolorallocatealpha to 127.
With imagecolorallocatealpha, it will allocate a color for an image.
Usage:
int imagecolorallocatealpha ( resource image, int red, int green, int blue, int alpha)
From PHP manual:
imagecolorallocatealpha() behaves identically to imagecolorallocate() with the addition of the transparency parameter alpha which may have a value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.
Returns FALSE if the allocation failed.
Before using it, you must set to false the blending mode for an image and set true the flag to save full alpha channel information.
Example:
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<?
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$newImg = imagecreatetruecolor($nWidth, $nHeight);
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imagealphablending($newImg, false);
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imagesavealpha($newImg,true);
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$transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
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imagefilledrectangle($newImg, 0, 0, $nWidth, $nHeight, $transparent);
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imagecopyresampled($newImg, $im, 0, 0, 0, 0, $nWidth, $nHeight, $imgInfo[0], $imgInfo[1]);
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?>
(more…)
Posted in coded | 9 Comments »
Sunday, May 25th, 2008
| Name |
Description |
ASCII() |
Return numeric value of left-most character |
BIN() |
Return a string representation of the argument |
BIT_LENGTH() |
Return length of argument in bits |
CHAR_LENGTH() |
Return number of characters in argument |
CHAR() |
Return the character for each integer passed |
CHARACTER_LENGTH() |
A synonym for CHAR_LENGTH() |
CONCAT_WS() |
Return concatenate with separator |
CONCAT() |
Return concatenated string |
ELT() |
Return string at index number |
EXPORT_SET() |
Return a string such that for every bit set in the value bits, you get an on string and for every unset bit, you get an off string |
FIELD() |
Return the index (position) of the first argument in the subsequent arguments |
FIND_IN_SET() |
Return the index position of the first argument within the second argument |
FORMAT() |
Return a number formatted to specified number of decimal places |
HEX() |
Return a hexadecimal representation of a decimal or string value |
INSERT() |
Insert a substring at the specified position up to the specified number of characters |
INSTR() |
Return the index of the first occurrence of substring |
LCASE() |
Synonym for LOWER() |
LEFT() |
Return the leftmost number of characters as specified |
LENGTH() |
Return the length of a string in bytes |
LIKE |
Simple pattern matching |
LOAD_FILE() |
Load the named file |
LOCATE() |
Return the position of the first occurrence of substring |
LOWER() |
Return the argument in lowercase |
LPAD() |
Return the string argument, left-padded with the specified string |
LTRIM() |
Remove leading spaces |
MAKE_SET() |
Return a set of comma-separated strings that have the corresponding bit in bits set |
MATCH |
Perform full-text search |
MID() |
Return a substring starting from the specified position |
NOT LIKE |
Negation of simple pattern matching |
NOT REGEXP |
Negation of REGEXP |
OCTET_LENGTH() |
A synonym for LENGTH() |
ORD() |
Return character code for leftmost character of the argument |
POSITION() |
A synonym for LOCATE() |
QUOTE() |
Escape the argument for use in an SQL statement |
REGEXP |
Pattern matching using regular expressions |
REPEAT() |
Repeat a string the specified number of times |
REPLACE() |
Replace occurrences of a specified string |
REVERSE() |
Reverse the characters in a string |
RIGHT() |
Return the specified rightmost number of characters |
RLIKE |
Synonym for REGEXP |
RPAD() |
Append string the specified number of times |
RTRIM() |
Remove trailing spaces |
SOUNDEX() |
Return a soundex string |
SOUNDS LIKE(v4.1.0) |
Compare sounds |
SPACE() |
Return a string of the specified number of spaces |
STRCMP() |
Compare two strings |
SUBSTR() |
Return the substring as specified |
SUBSTRING_INDEX() |
Return a substring from a string before the specified number of occurrences of the delimiter |
SUBSTRING() |
Return the substring as specified |
TRIM() |
Remove leading and trailing spaces |
UCASE() |
Synonym for UPPER() |
UNHEX()(v4.1.2) |
Convert each pair of hexadecimal digits to a character |
UPPER() |
Convert to uppercase |
String-valued functions return NULL if the length of the result would be greater than the value of the max_allowed_packet system variable.
For functions that operate on string positions, the first position is numbered 1.
(more…)
Posted in coded | No Comments »
Friday, May 16th, 2008
PHP allows you to write code in two flavours, one is procedural and the other
is object oriented. You can even write procedural code in PHP5 and it will run
without any problems. If you are not clear about procedural and object oriented
programming, then we will have a look at these two different coding styles. The
following two examples are not fully running examples rather a pseudo code:
<?
$user_input = $_POST[‘field‘];
$filtered_content = filter($user_input); //user input filtering
mysql_connect(”dbhost”,”dbuser”,”dbpassword”); //database
mysql_select_db(”dbname”);
$sql = “some query”;
$result = mysql_query($sql);
while ($data = mysql_fetch_assoc())
{
process ($data);
}
process_user_input($filtered_content);
?>
You will notice using a lot of inline processing either directly or via using functions.
It may stand as an example of typical procedural operation. Let’s see how it looks
after converting it to OOP:
<?
$input_filter = new filter();
$input_filter->filter_user_input(); //filter the user inputs
$db = new dal(”mysql”); //data access layer
$db->connect($dbconfig); //using mysql
$result = $db->execute($sql);
ReportGenerator::makereport($result); //process data
$model = new Postmodel($filter->get_filtered_content());
$model->insert();
?>
Now if you take a look into these two code snippets, you will find that the latter
one is much more readable. Well, you can make the first one more readable by
introducing some more functions into it, but how many functions are you ready
to search into when you use them? The latter snippet is better organized because
you know which object is handling which process. If you write big applications in
procedural style, it will be almost impossible to manage after a few versions. Of
course you can implement strict coding conventions, but it is agreed by millions
of developers that it won’t give you the ultimate manageability and usability if it’s
procedural unless you do it in OO style. Almost all big applications are written using
the object oriented approach. (more…)
Posted in coded | No Comments »
