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.