MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
          Returns the Performance Schema thread ID assigned to a given
          connection ID, or the thread ID for the current connection if
          the connection ID is NULL.
        
                in_connection_id BIGINT UNSIGNED: The
                ID of the connection for which to return the thread ID.
                This is a value of the type given in the
                PROCESSLIST_ID column of the
                Performance Schema threads
                table or the Id column of
                SHOW PROCESSLIST output.