For read and write adapters, fetchOne(), fetchAll(), fetchAssoc(), fetchRow(), fetchCol(), fetchPairs(), see lib\Zend\Db\Adapter\Abstract.php

Also, standalone class lib\Mage\DB\Mysqli.php has interesting methods.

Zend

For fetchAll(), fetchColumn(), fetchObject(): app/code/core/Zend/Db/Statement.php

By default, fetchAll() returns an array of rows, each of which is an associative array. The keys of the associative array are the columns or column aliases named in the select query.

You can specify a different style of fetching results using the setFetchMode() method. The modes supported are identified by constants:

Zend_Db::FETCH_ASSOC: return data in an array of associative arrays. The array keys are column names, as strings. This is the default fetch mode for Zend_Db_Adapter classes.

Note that if your select-list contains more than one column with the same name, for example if they are from two different tables in a JOIN, there can be only one entry in the associative array for a given name. If you use the FETCH_ASSOC mode, you should specify column aliases in your SELECT query to ensure that the names result in unique array keys.

By default, these strings are returned as they are returned by the database driver. This is typically the spelling of the column in the RDBMS server. You can specify the case for these strings, using the Zend_Db::CASE_FOLDING option. Specify this when instantiating the Adapter. See this example

Zend_Db::FETCH_NUM: return data in an array of arrays. The arrays are indexed by integers, corresponding to the position of the respective field in the select-list of the query.

Zend_Db::FETCH_BOTH: return data in an array of arrays. The array keys are both strings as used in the FETCH_ASSOC mode, and integers as used in the FETCH_NUM mode. Note that the number of elements in the array is double that which would be in the array if you used either FETCH_ASSOC or FETCH_NUM.

Zend_Db::FETCH_COLUMN: return data in an array of values. The value in each array is the value returned by one column of the result set. By default, this is the first column, indexed by 0.

Zend_Db::FETCH_OBJ: return data in an array of objects. The default class is the PHP built-in class stdClass. Columns of the result set are available as public properties of the object.