The TABLE_CONSTRAINTS_EXTENSIONS table (available as of MySQL 8.0.21) provides information about table constraint attributes defined for primary and secondary storage engines.
The TABLE_CONSTRAINTS_EXTENSIONS table is reserved for future use.
The TABLE_CONSTRAINTS_EXTENSIONS table has these columns:
CONSTRAINT_CATALOG
The name of the catalog to which the table belongs.
CONSTRAINT_SCHEMA
The name of the schema (database) to which the table belongs.
CONSTRAINT_NAME
The name of the constraint.
TABLE_NAME
The name of the table.
ENGINE_ATTRIBUTE
Constraint attributes defined for the primary storage engine. Reserved for future use.
SECONDARY_ENGINE_ATTRIBUTE
Constraint attributes defined for the secondary storage engine. Reserved for future use.