Tag Archives: Insert

Computer Algorithms: Linked List

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Introduction

The linked list is a data structure in which the items are ordered in a linear way. Although modern programming languages support very flexible and rich libraries that works with arrays, which use arrays to represent lists, the principles of building a linked list remain very important. The way linked lists are implemented is a ground level in order to build more complex data structures such as trees.

It’s true that almost every operation we can perform on a linked list can be done with an array. It’s also true that some operations can be faster on arrays compared to linked lists.

However understanding how to implement the basic operations of a linked list such as INSERT, DELETE, INSERT_AFTER, PRINT and so on is crucial in order to implement data structures as rooted trees, B-trees, red-black trees, etc.

Overview

Unlike arrays where we don’t have pointers to the next and the previous item, the linked list is designed to support such pointers. In some implementations there is only one pointer pointing to the successor of the item. This kind of data structures are called singly linked lists. In this case the the last element doesn’t have a successor, so the pointer to its next element usualy is NULL. However the most implemented version of a linked list supports two pointers. These are the so called doubly linked lists.

Arrays vs. linked list
Arrays items are defined by their indices, while the linked list item contains a pointer to its predecessor and his successor!
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How to Dump the Generated Zend_Db SQL Query

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The Typical PHP Approach

Typically a PHP programmer will write his SQL query as a string and will execute it via mysql_query.

$sql = "SELECT * FROM my_table";
$resource = mysql_query($sql);

So eventually when you want to dump this “complex” query, or whatever query there is, you can simply “echo” it and see what’s its syntax.

// this query is WRONG because of the where clause
$sql = "SELECT * FROM my_table WHERE id = ";
 
// dump and debug the wrong query
die($sql);
 
// this line won't be executed
$resource = mysql_query($sql);

So far so good, but things appear to be a bit different when you start to work with Zend Framework. Higher levels of abstraction come with slightly more difficult ways to dump (debug) your SQL queries.

OK you’ve two options. Using Zend_Db_Select or … not.
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MySQL Expressions in Zend Framework

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If you’re a Zend Framework developer, you’d know the built-in Zend_Db_Table methods insert(), update(), etc.

However the general approach there is like is said:

$data = array();
$data['key'] = $value;
$model = new ModelName();
$model->insert($data);
 
// that's very basic example, but in general this is 
// the way it works.

What happens if one of the column have to be an MySQL expression!? In example you’ve a date field and you’d like to insert something like the MySQL’s method NOW().

The solution is simply call a Zend_Db_Expr.

$data = array();
$data['key'] = $value;
$data['date'] = new Zend_Db_Expr('NOW()');
$model = new ModelName();
$model->insert($data);
 
// now the date column will be NOWed :)