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<?php
// $Id$
/**
* @file
* Select builder for PostgreSQL database engine.
*/
/**
* @ingroup database
* @{
*/
class SelectQuery_pgsql extends SelectQuery {
public function orderRandom() {
$alias = $this->addExpression('RANDOM()', 'random_field');
$this->orderBy($alias);
return $this;
}
/**
* Overrides SelectQuery::orderBy().
*
* PostgreSQL adheres strictly to the SQL-92 standard and requires that when
* using DISTINCT or GROUP BY conditions, fields and expressions that are
* ordered on also need to be selected. This is a best effort implementation
* to handle the cases that can be automated by adding the field if it is not
* yet selected.
*
* @code
* $query = db_select('node', 'n');
* $query->join('node_revision', 'nr', 'n.vid = nr.vid');
* $query
* ->distinct()
* ->fields('n')
* ->orderBy('timestamp');
* @endcode
*
* In this query, it is not possible (without relying on the schema) to know
* whether timestamp belongs to node_revisions and needs to be added or
* belongs to node and is already selected. Queries like this will need to be
* corrected in the original query by adding an explicit call to
* SelectQuery::addField() or SelectQuery::fields().
*
* Since this has a small performance impact, both by the additional
* processing in this function and in the database that needs to return the
* additional fields, this is done as an override instead of implementing it
* directly in SelectQuery::orderBy().
*/
public function orderBy($field, $direction = 'ASC') {
// Call parent function to order on this.
$return = parent::orderBy($field, $direction);
// If there is a table alias specified, split it up.
if (strpos($field, '.') !== FALSE) {
list($table, $table_field) = explode('.', $field);
}
// Figure out if the field has already been added.
foreach ($this->fields as $existing_field) {
if (!empty($table)) {
// If table alias is given, check if field and table exists.
if ($existing_field['table'] == $table && $existing_field['field'] == $table_field) {
return $return;
}
}
else {
// If there is no table, simply check if the field exists as a field or
// an aliased field.
if ($existing_field['alias'] == $field) {
return $return;
}
}
}
// Also check expression aliases.
foreach ($this->expressions as $expression) {
if ($expression['alias'] == $field) {
return $return;
}
}
// If a table loads all fields, it can not be added again. It would
// result in an ambigious alias error because that field would be loaded
// twice: Once through table_alias.* and once directly. If the field
// actually belongs to a different table, it must be added manually.
foreach ($this->tables as $table) {
if (!empty($table['all_fields'])) {
return $return;
}
}
// If $field contains an characters which are not allowed in a field name
// it is considered an expression, these can't be handeld automatically
// either.
if ($this->connection->escapeField($field) != $field) {
return $return;
}
// This is a case that can be handled automatically, add the field.
$this->addField(NULL, $field);
return $return;
}
}
/**
* @} End of "ingroup database".
*/
|
