= $limits;

		$this->request = "{$this->sql_clauses['select']} {$this->sql_clauses['from']} {$where} {$this->sql_clauses['orderby']} {$this->sql_clauses['limits']}";

		// $args can be anything. Only use the args defined in defaults to compute the key.
		$key = md5( serialize( wp_array_slice_assoc( $args, array_keys( $this->query_var_defaults ) ) ) . serialize( $taxonomies ) . $this->request );
		$last_changed = wp_cache_get_last_changed( 'terms' );
		$cache_key = "get_terms:$key:$last_changed";
		$cache = wp_cache_get( $cache_key, 'terms' );
		if ( false !== $cache ) {
			if ( 'all' === $_fields || 'all_with_object_id' === $_fields ) {
				$cache = $this->populate_terms( $cache );
			}

			$this->terms = $cache;
			return $this->terms;
		}

		if ( 'count' == $_fields ) {
			$count = $wpdb->get_var( $this->request );
			wp_cache_set( $cache_key, $count, 'terms' );
			return $count;
		}

		$terms = $wpdb->get_results( $this->request );
		if ( 'all' == $_fields || 'all_with_object_id' === $_fields ) {
			update_term_cache( $terms );
		}

		// Prime termmeta cache.
		if ( $args['update_term_meta_cache'] ) {
			$term_ids = wp_list_pluck( $terms, 'term_id' );
			update_termmeta_cache( $term_ids );
		}

		if ( empty( $terms ) ) {
			wp_cache_add( $cache_key, array(), 'terms', DAY_IN_SECONDS );
			return array();
		}

		if ( $child_of ) {
			foreach ( $taxonomies as $_tax ) {
				$children = _get_term_hierarchy( $_tax );
				if ( ! empty( $children ) ) {
					$terms = _get_term_children( $child_of, $terms, $_tax );
				}
			}
		}

		// Update term counts to include children.
		if ( $args['pad_counts'] && 'all' == $_fields ) {
			foreach ( $taxonomies as $_tax ) {
				_pad_term_counts( $terms, $_tax );
			}
		}

		// Make sure we show empty categories that have children.
		if ( $hierarchical && $args['hide_empty'] && is_array( $terms ) ) {
			foreach ( $terms as $k => $term ) {
				if ( ! $term->count ) {
					$children = get_term_children( $term->term_id, $term->taxonomy );
					if ( is_array( $children ) ) {
						foreach ( $children as $child_id ) {
							$child = get_term( $child_id, $term->taxonomy );
							if ( $child->count ) {
								continue 2;
							}
						}
					}

					// It really is empty.
					unset( $terms[ $k ] );
				}
			}
		}

		/*
		 * When querying for terms connected to objects, we may get
		 * duplicate results. The duplicates should be preserved if
		 * `$fields` is 'all_with_object_id', but should otherwise be
		 * removed.
		 */
		if ( ! empty( $args['object_ids'] ) && 'all_with_object_id' != $_fields ) {
			$_tt_ids = $_terms = array();
			foreach ( $terms as $term ) {
				if ( isset( $_tt_ids[ $term->term_id ] ) ) {
					continue;
				}

				$_tt_ids[ $term->term_id ] = 1;
				$_terms[] = $term;
			}

			$terms = $_terms;
		}

		$_terms = array();
		if ( 'id=>parent' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[ $term->term_id ] = $term->parent;
			}
		} elseif ( 'ids' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[] = (int) $term->term_id;
			}
		} elseif ( 'tt_ids' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[] = (int) $term->term_taxonomy_id;
			}
		} elseif ( 'names' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[] = $term->name;
			}
		} elseif ( 'slugs' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[] = $term->slug;
			}
		} elseif ( 'id=>name' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[ $term->term_id ] = $term->name;
			}
		} elseif ( 'id=>slug' == $_fields ) {
			foreach ( $terms as $term ) {
				$_terms[ $term->term_id ] = $term->slug;
			}
		}

		if ( ! empty( $_terms ) ) {
			$terms = $_terms;
		}

		// Hierarchical queries are not limited, so 'offset' and 'number' must be handled now.
		if ( $hierarchical && $number && is_array( $terms ) ) {
			if ( $offset >= count( $terms ) ) {
				$terms = array();
			} else {
				$terms = array_slice( $terms, $offset, $number, true );
			}
		}

		wp_cache_add( $cache_key, $terms, 'terms', DAY_IN_SECONDS );

		if ( 'all' === $_fields || 'all_with_object_id' === $_fields ) {
			$terms = $this->populate_terms( $terms );
		}

		$this->terms = $terms;
		return $this->terms;
	}

	/**
	 * Parse and sanitize 'orderby' keys passed to the term query.
	 *
	 * @since 4.6.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param string $orderby_raw Alias for the field to order by.
	 * @return string|false Value to used in the ORDER clause. False otherwise.
	 */
	protected function parse_orderby( $orderby_raw ) {
		$_orderby = strtolower( $orderby_raw );
		$maybe_orderby_meta = false;

		if ( in_array( $_orderby, array( 'term_id', 'name', 'slug', 'term_group' ), true ) ) {
			$orderby = "t.$_orderby";
		} elseif ( in_array( $_orderby, array( 'count', 'parent', 'taxonomy', 'term_taxonomy_id', 'description' ), true ) ) {
			$orderby = "tt.$_orderby";
		} elseif ( 'term_order' === $_orderby ) {
			$orderby = 'tr.term_order';
		} elseif ( 'include' == $_orderby && ! empty( $this->query_vars['include'] ) ) {
			$include = implode( ',', wp_parse_id_list( $this->query_vars['include'] ) );
			$orderby = "FIELD( t.term_id, $include )";
		} elseif ( 'slug__in' == $_orderby && ! empty( $this->query_vars['slug'] ) && is_array( $this->query_vars['slug'] ) ) {
			$slugs = implode( "', '", array_map( 'sanitize_title_for_query', $this->query_vars['slug'] ) );
			$orderby = "FIELD( t.slug, '" . $slugs . "')";
		} elseif ( 'none' == $_orderby ) {
			$orderby = '';
		} elseif ( empty( $_orderby ) || 'id' == $_orderby || 'term_id' === $_orderby ) {
			$orderby = 't.term_id';
		} else {
			$orderby = 't.name';

			// This may be a value of orderby related to meta.
			$maybe_orderby_meta = true;
		}

		/**
		 * Filters the ORDERBY clause of the terms query.
		 *
		 * @since 2.8.0
		 *
		 * @param string $orderby    `ORDERBY` clause of the terms query.
		 * @param array  $args       An array of terms query arguments.
		 * @param array  $taxonomies An array of taxonomies.
		 */
		$orderby = apply_filters( 'get_terms_orderby', $orderby, $this->query_vars, $this->query_vars['taxonomy'] );

		// Run after the 'get_terms_orderby' filter for backward compatibility.
		if ( $maybe_orderby_meta ) {
			$maybe_orderby_meta = $this->parse_orderby_meta( $_orderby );
			if ( $maybe_orderby_meta ) {
				$orderby = $maybe_orderby_meta;
			}
		}

		return $orderby;
	}

	/**
	 * Generate the ORDER BY clause for an 'orderby' param that is potentially related to a meta query.
	 *
	 * @since 4.6.0
	 *
	 * @param string $orderby_raw Raw 'orderby' value passed to WP_Term_Query.
	 * @return string ORDER BY clause.
	 */
	protected function parse_orderby_meta( $orderby_raw ) {
		$orderby = '';

		// Tell the meta query to generate its SQL, so we have access to table aliases.
		$this->meta_query->get_sql( 'term', 't', 'term_id' );
		$meta_clauses = $this->meta_query->get_clauses();
		if ( ! $meta_clauses || ! $orderby_raw ) {
			return $orderby;
		}

		$allowed_keys = array();
		$primary_meta_key = null;
		$primary_meta_query = reset( $meta_clauses );
		if ( ! empty( $primary_meta_query['key'] ) ) {
			$primary_meta_key = $primary_meta_query['key'];
			$allowed_keys[] = $primary_meta_key;
		}
		$allowed_keys[] = 'meta_value';
		$allowed_keys[] = 'meta_value_num';
		$allowed_keys   = array_merge( $allowed_keys, array_keys( $meta_clauses ) );

		if ( ! in_array( $orderby_raw, $allowed_keys, true ) ) {
			return $orderby;
		}

		switch( $orderby_raw ) {
			case $primary_meta_key:
			case 'meta_value':
				if ( ! empty( $primary_meta_query['type'] ) ) {
					$orderby = "CAST({$primary_meta_query['alias']}.meta_value AS {$primary_meta_query['cast']})";
				} else {
					$orderby = "{$primary_meta_query['alias']}.meta_value";
				}
				break;

			case 'meta_value_num':
				$orderby = "{$primary_meta_query['alias']}.meta_value+0";
				break;

			default:
				if ( array_key_exists( $orderby_raw, $meta_clauses ) ) {
					// $orderby corresponds to a meta_query clause.
					$meta_clause = $meta_clauses[ $orderby_raw ];
					$orderby = "CAST({$meta_clause['alias']}.meta_value AS {$meta_clause['cast']})";
				}
				break;
		}

		return $orderby;
	}

	/**
	 * Parse an 'order' query variable and cast it to ASC or DESC as necessary.
	 *
	 * @since 4.6.0
	 *
	 * @param string $order The 'order' query variable.
	 * @return string The sanitized 'order' query variable.
	 */
	protected function parse_order( $order ) {
		if ( ! is_string( $order ) || empty( $order ) ) {
			return 'DESC';
		}

		if ( 'ASC' === strtoupper( $order ) ) {
			return 'ASC';
		} else {
			return 'DESC';
		}
	}

	/**
	 * Used internally to generate a SQL string related to the 'search' parameter.
	 *
	 * @since 4.6.0
	 *
	 * @global wpdb $wpdb WordPress database abstraction object.
	 *
	 * @param string $string
	 * @return string
	 */
	protected function get_search_sql( $string ) {
		global $wpdb;

		$like = '%' . $wpdb->esc_like( $string ) . '%';

		return $wpdb->prepare( '((t.name LIKE %s) OR (t.slug LIKE %s))', $like, $like );
	}

	/**
	 * Creates an array of term objects from an array of term IDs.
	 *
	 * Also discards invalid term objects.
	 *
	 * @since 4.9.8
	 *
	 * @param array $term_ids Term IDs.
	 * @return array
	 */
	protected function populate_terms( $term_ids ) {
		$terms = array();

		if ( ! is_array( $term_ids ) ) {
			return $terms;
		}

		foreach ( $term_ids as $key => $term_id ) {
			$term = get_term( $term_id );
			if ( $term instanceof WP_Term ) {
				$terms[ $key ] = $term;
			}
		}

		return $terms;
	}
}