<?php

/**

 * @file

 * Select builder for PostgreSQL database engine.

 */

/**

 * @addtogroup 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 ambiguous 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 handled 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 "addtogroup database".

 */