Syntax:
SET variable = expr [, variable = expr] ...

variable: {
    user_var_name
  | param_name
  | local_var_name
  | {GLOBAL | @@GLOBAL.} system_var_name
  | {PERSIST | @@PERSIST.} system_var_name
  | {PERSIST_ONLY | @@PERSIST_ONLY.} system_var_name
  | [SESSION | @@SESSION. | @@] system_var_name
}

SET syntax for variable assignment enables you to assign values to
different types of variables that affect the operation of the server or
clients:

o User-defined variables. See
  https://dev.mysql.com/doc/refman/8.0/en/user-variables.html.

o Stored procedure and function parameters, and stored program local
  variables. See
  https://dev.mysql.com/doc/refman/8.0/en/stored-program-variables.html
  .

o System variables. See
  https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html.
  System variables also can be set at server startup, as described in
  https://dev.mysql.com/doc/refman/8.0/en/using-system-variables.html.

URL: https://dev.mysql.com/doc/refman/8.0/en/set-variable.html

