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