View source for Accessing the database using JDatabase

==Preparing the query==
<source lang="php">
// Get a database object
$db = JFactory::getDBO();

$query = "SELECT * FROM #__example_table WHERE id = 999999;";
$db->setQuery($query);
</source>

First we instantiate the database object; then we prepare the query. You can use the normal SQL syntax. The only thing you have to change is the table prefix. To make this as flexible as possible, Joomla uses a placeholder for the prefix, the &ldquo;#__&rdquo;. In the next step, the $db->setQuery(), this string is replaced with the correct prefix.

Now, if we don't want to get information from the database, but rather insert a row into it, we need one more function. Every string value in the SQL syntax should be quoted. For example, MySQL uses backticks &#096;&#096; for names and single quotes &lsquo;&lsquo; for values. Joomla has some functions to do this for us and to ensure code compatibility between different databases. We can pass the names to the function $db->nameQuote($name) and the values to the function $db->Quote($value). 

A fully quoted query example is:
<source lang="php">
$query = "
  SELECT * 
    FROM ".$db->nameQuote('#__example_table')."  
    WHERE ".$db->nameQuote('id')." = ".$db->quote('999999').";
  ";
</source>

Whatever we want to do, we have to set the query with the $db->setQuery() function. Although you could write the query directly as a parameter for $db->setQuery(), it's commonly done by first saving it in a variable, normally $query, and then handing this variable over. This results in clean, readable code.

==== setQuery($query) ====
The ''setQuery($query)'' method sets up a database query for later execution either by the query() method or one of the Load result methods.
<source lang="php">
$db = JFactory::getDBO();
$query = "/* some valid sql string */";
$db->setQuery($query);
</source>

Notes:
The parameter $query must be a valid SQL string. It can either be added as a string parameter or as a variable. Generally a variable is preferred; it leads to more legible code and can help in debugging.

setQuery() also takes three other parameters: $offset, $limit (both used in list pagination) and $prefix, an alternative table prefix. All three variables have default values set and can usually be ignored.