information_schema.statistics.index_schema

mysql

type: VARCHAR NOT NULL
5.7-8

mariadb

type: NULL
Note:
Database name.
© 2022 MariaDB
5.1-10.8
type: VARCHAR NOT NULL
Note:
Database name.
© 2022 MariaDB
10.2-10.7

tidb

type: VARCHAR(64) NULL
Note:
The name of the database to which the index belongs.
© 2022 PingCAP
4-6.1

postgres

cockroachdb

type: unknown
Note:
Name of the database that contains the index.
© 2022 CockroachDB
1-21.2

mssql