REGEXP':
						$operator = $meta_compare_key;
						if ( isset( $clause['type_key'] ) && 'BINARY' === strtoupper( $clause['type_key'] ) ) {
							$cast     = 'BINARY';
							$meta_key = "CAST($subquery_alias.meta_key AS BINARY)";
						} else {
							$cast     = '';
							$meta_key = "$subquery_alias.meta_key";
						}

						$meta_compare_string = $meta_compare_string_start . "AND $meta_key REGEXP $cast %s " . $meta_compare_string_end;
						$where               = $wpdb->prepare( $meta_compare_string, $clause['key'] ); // phpcs:ignore WordPress.DB.PreparedSQL.NotPrepared
						break;
				}

				$sql_chunks['where'][] = $where;
			}
		}

		// meta_value.
		if ( array_key_exists( 'value', $clause ) ) {
			$meta_value = $clause['value'];

			if ( in_array( $meta_compare, array( 'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN' ), true ) ) {
				if ( ! is_array( $meta_value ) ) {
					$meta_value = preg_split( '/[,\s]+/', $meta_value );
				}
			} elseif ( is_string( $meta_value ) ) {
				$meta_value = trim( $meta_value );
			}

			switch ( $meta_compare ) {
				case 'IN':
				case 'NOT IN':
					$meta_compare_string = '(' . substr( str_repeat( ',%s', count( $meta_value ) ), 1 ) . ')';
					$where               = $wpdb->prepare( $meta_compare_string, $meta_value );
					break;

				case 'BETWEEN':
				case 'NOT BETWEEN':
					$where = $wpdb->prepare( '%s AND %s', $meta_value[0], $meta_value[1] );
					break;

				case 'LIKE':
				case 'NOT LIKE':
					$meta_value = '%' . $wpdb->esc_like( $meta_value ) . '%';
					$where      = $wpdb->prepare( '%s', $meta_value );
					break;

				// EXISTS with a value is interpreted as '='.
				case 'EXISTS':
					$meta_compare = '=';
					$where        = $wpdb->prepare( '%s', $meta_value );
					break;

				// 'value' is ignored for NOT EXISTS.
				case 'NOT EXISTS':
					$where = '';
					break;

				default:
					$where = $wpdb->prepare( '%s', $meta_value );
					break;

			}

			if ( $where ) {
				if ( 'CHAR' === $meta_type ) {
					$sql_chunks['where'][] = "$alias.meta_value {$meta_compare} {$where}";
				} else {
					$sql_chunks['where'][] = "CAST($alias.meta_value AS {$meta_type}) {$meta_compare} {$where}";
				}
			}
		}

		/*
		 * Multiple WHERE clauses (for meta_key and meta_value) should
		 * be joined in parentheses.
		 */
		if ( 1 < count( $sql_chunks['where'] ) ) {
			$sql_chunks['where'] = array( '( ' . implode( ' AND ', $sql_chunks['where'] ) . ' )' );
		}

		return $sql_chunks;
	}

	/**
	 * Gets a flattened list of sanitized meta clauses.
	 *
	 * This array should be used for clause lookup, as when the table alias and CAST type must be determined for
	 * a value of 'orderby' corresponding to a meta clause.
	 *
	 * @since 4.2.0
	 *
	 * @return array Meta clauses.
	 */
	public function get_clauses() {
		return $this->clauses;
	}

	/**
	 * Identifies an existing table alias that is compatible with the current
	 * query clause.
	 *
	 * We avoid unnecessary table joins by allowing each clause to look for
	 * an existing table alias that is compatible with the query that it
	 * needs to perform.
	 *
	 * An existing alias is compatible if (a) it is a sibling of `$clause`
	 * (ie, it's under the scope of the same relation), and (b) the combination
	 * of operator and relation between the clauses allows for a shared table join.
	 * In the case of WP_Meta_Query, this only applies to 'IN' clauses that are
	 * connected by the relation 'OR'.
	 *
	 * @since 4.1.0
	 *
	 * @param array $clause       Query clause.
	 * @param array $parent_query Parent query of $clause.
	 * @return string|false Table alias if found, otherwise false.
	 */
	protected function find_compatible_table_alias( $clause, $parent_query ) {
		$alias = false;

		foreach ( $parent_query as $sibling ) {
			// If the sibling has no alias yet, there's nothing to check.
			if ( empty( $sibling['alias'] ) ) {
				continue;
			}

			// We're only interested in siblings that are first-order clauses.
			if ( ! is_array( $sibling ) || ! $this->is_first_order_clause( $sibling ) ) {
				continue;
			}

			$compatible_compares = array();

			// Clauses connected by OR can share joins as long as they have "positive" operators.
			if ( 'OR' === $parent_query['relation'] ) {
				$compatible_compares = array( '=', 'IN', 'BETWEEN', 'LIKE', 'REGEXP', 'RLIKE', '>', '>=', '<', '<=' );

				// Clauses joined by AND with "negative" operators share a join only if they also share a key.
			} elseif ( isset( $sibling['key'] ) && isset( $clause['key'] ) && $sibling['key'] === $clause['key'] ) {
				$compatible_compares = array( '!=', 'NOT IN', 'NOT LIKE' );
			}

			$clause_compare  = strtoupper( $clause['compare'] );
			$sibling_compare = strtoupper( $sibling['compare'] );
			if ( in_array( $clause_compare, $compatible_compares, true ) && in_array( $sibling_compare, $compatible_compares, true ) ) {
				$alias = preg_replace( '/\W/', '_', $sibling['alias'] );
				break;
			}
		}

		/**
		 * Filters the table alias identified as compatible with the current clause.
		 *
		 * @since 4.1.0
		 *
		 * @param string|false  $alias        Table alias, or false if none was found.
		 * @param array         $clause       First-order query clause.
		 * @param array         $parent_query Parent of $clause.
		 * @param WP_Meta_Query $query        WP_Meta_Query object.
		 */
		return apply_filters( 'meta_query_find_compatible_table_alias', $alias, $clause, $parent_query, $this );
	}

	/**
	 * Checks whether the current query has any OR relations.
	 *
	 * In some cases, the presence of an OR relation somewhere in the query will require
	 * the use of a `DISTINCT` or `GROUP BY` keyword in the `SELECT` clause. The current
	 * method can be used in these cases to determine whether such a clause is necessary.
	 *
	 * @since 4.3.0
	 *
	 * @return bool True if the query contains any `OR` relations, otherwise false.
	 */
	public function has_or_relation() {
		return $this->has_or_relation;
	}
}