MySQL:

CURRENT_USER

Syntax:
CURRENT_USER, CURRENT_USER()

Returns the user name and host name combination for the MySQL account
that the server used to authenticate the current client. This account
determines your access privileges. The return value is a string in the
utf8 character set.

The value of CURRENT_USER() can differ from the value of USER().

URL: https://dev.mysql.com/doc/refman/8.0/en/information-functions.html

Example

mysql> SELECT USER();
-> 'davida@localhost'
mysql> SELECT * FROM mysql.user;
ERROR 1044: Access denied for user ''@'localhost' to
database 'mysql'
mysql> SELECT CURRENT_USER();
-> '@localhost'