information_schema.tables.data_free

mysql

type: BIGINT NULL
5.7-8

mariadb

type: NULL
Note:
Bytes allocated but unused. For InnoDB tables in a shared tablespace, the free space of the shared tablespace with small safety margin. An estimate in the case of partitioned tables - see the PARTITIONS table.
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5.1-10.8

tidb

type: BIGINT(21) NULL
Note:
Data fragment. The value is currently 0.
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4-6.1

postgres

cockroachdb

mssql