ATTRDEFAULTFETCHMODE

ATTR_DEFAULT_FETCH_MODE is a constant used in the PHP Data Objects (PDO) extension. It defines the default fetch mode for results produced by PDO statements, unless a fetch mode is explicitly specified in a fetch call. The attribute is set on a PDO instance using setAttribute.

Setting ATTR_DEFAULT_FETCH_MODE changes how fetch and fetchAll return data when no specific mode is given. Common fetch modes include FETCH_ASSOC (return an associative array), FETCH_NUM (return a numeric array), FETCH_BOTH (return both associative and numeric indices), and FETCH_OBJ (return an anonymous object with properties named after the column names). The default behavior if the attribute is not changed is FETCH_BOTH.

To apply a default, you typically use code like: $pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC); After this, $stmt = $pdo->query("SELECT id, name FROM users"); $row = $stmt->fetch(); will yield an associative array with keys 'id' and 'name'. The default fetch mode can be overridden at any time by calling fetch with an explicit mode or by using a statement-specific setFetchMode.

Considerations include memory usage and readability. Using FETCH_ASSOC often provides clearer code and reduces memory overhead compared to FETCH_BOTH when large result sets are involved. For very large results, fetching row by row with fetch() can be more memory-efficient than fetchAll().

Related topics include the PDO class, individual fetch modes, and the fetch methods of PDOStatement.