Source

File: wp-includes/wp-db.php

public function query( $query ) {
		if ( ! $this->ready ) {
			$this->check_current_query = true;
			return false;
		}

		/**
		 * Filters the database query.
		 *
		 * Some queries are made before the plugins have been loaded,
		 * and thus cannot be filtered with this method.
		 *
		 * @since 2.1.0
		 *
		 * @param string $query Database query.
		 */
		$query = apply_filters( 'query', $query );

		$this->flush();

		// Log how the function was called.
		$this->func_call = "\$db->query(\"$query\")";

		// If we're writing to the database, make sure the query will write safely.
		if ( $this->check_current_query && ! $this->check_ascii( $query ) ) {
			$stripped_query = $this->strip_invalid_text_from_query( $query );
			// strip_invalid_text_from_query() can perform queries, so we need
			// to flush again, just to make sure everything is clear.
			$this->flush();
			if ( $stripped_query !== $query ) {
				$this->insert_id = 0;
				return false;
			}
		}

		$this->check_current_query = true;

		// Keep track of the last query for debug.
		$this->last_query = $query;

		$this->_do_query( $query );

		// MySQL server has gone away, try to reconnect.
		$mysql_errno = 0;
		if ( ! empty( $this->dbh ) ) {
			if ( $this->use_mysqli ) {
				if ( $this->dbh instanceof mysqli ) {
					$mysql_errno = mysqli_errno( $this->dbh );
				} else {
					// $dbh is defined, but isn't a real connection.
					// Something has gone horribly wrong, let's try a reconnect.
					$mysql_errno = 2006;
				}
			} else {
				if ( is_resource( $this->dbh ) ) {
					$mysql_errno = mysql_errno( $this->dbh );
				} else {
					$mysql_errno = 2006;
				}
			}
		}

		if ( empty( $this->dbh ) || 2006 === $mysql_errno ) {
			if ( $this->check_connection() ) {
				$this->_do_query( $query );
			} else {
				$this->insert_id = 0;
				return false;
			}
		}

		// If there is an error then take note of it.
		if ( $this->use_mysqli ) {
			if ( $this->dbh instanceof mysqli ) {
				$this->last_error = mysqli_error( $this->dbh );
			} else {
				$this->last_error = __( 'Unable to retrieve the error message from MySQL' );
			}
		} else {
			if ( is_resource( $this->dbh ) ) {
				$this->last_error = mysql_error( $this->dbh );
			} else {
				$this->last_error = __( 'Unable to retrieve the error message from MySQL' );
			}
		}

		if ( $this->last_error ) {
			// Clear insert_id on a subsequent failed insert.
			if ( $this->insert_id && preg_match( '/^\s*(insert|replace)\s/i', $query ) ) {
				$this->insert_id = 0;
			}

			$this->print_error();
			return false;
		}

		if ( preg_match( '/^\s*(create|alter|truncate|drop)\s/i', $query ) ) {
			$return_val = $this->result;
		} elseif ( preg_match( '/^\s*(insert|delete|update|replace)\s/i', $query ) ) {
			if ( $this->use_mysqli ) {
				$this->rows_affected = mysqli_affected_rows( $this->dbh );
			} else {
				$this->rows_affected = mysql_affected_rows( $this->dbh );
			}
			// Take note of the insert_id.
			if ( preg_match( '/^\s*(insert|replace)\s/i', $query ) ) {
				if ( $this->use_mysqli ) {
					$this->insert_id = mysqli_insert_id( $this->dbh );
				} else {
					$this->insert_id = mysql_insert_id( $this->dbh );
				}
			}
			// Return number of rows affected.
			$return_val = $this->rows_affected;
		} else {
			$num_rows = 0;
			if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
				while ( $row = mysqli_fetch_object( $this->result ) ) {
					$this->last_result[ $num_rows ] = $row;
					$num_rows++;
				}
			} elseif ( is_resource( $this->result ) ) {
				while ( $row = mysql_fetch_object( $this->result ) ) {
					$this->last_result[ $num_rows ] = $row;
					$num_rows++;
				}
			}

			// Log and return the number of rows selected.
			$this->num_rows = $num_rows;
			$return_val     = $num_rows;
		}

		return $return_val;
	}