MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4
      The TABLE_CONSTRAINTS_EXTENSIONS
      table 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.