`information_schema.user_variables.*`

show items implemented by

any at least two only one database all databases

relation	column	mysql	mariadb	tidb	postgres	cockroachdb	mssql
`user_variables`
	`character_set_name`	unsupported	`NULL`: 10.2-10.8	unsupported	unsupported	unsupported	unsupported
	`variable_name`	unsupported	`VARCHAR NOT NULL`: 10.2-10.7 `NULL`: 10.2-10.8	unsupported	unsupported	unsupported	unsupported
	`variable_type`	unsupported	`VARCHAR NOT NULL`: 10.2-10.7 `NULL`: 10.2-10.8	unsupported	unsupported	unsupported	unsupported
	`variable_value`	unsupported	`NULL`: 10.2-10.8	unsupported	unsupported	unsupported	unsupported