Database Normalization - Can one field point to another?
Even if SQL were to support a "pointer" like you describe, the pointer itself would take some memory. Ironically, the pointer might even be larger than the integer value it points to.

You tagged this question with MySQL, so I'll answer with respect to MySQL: there is no support for this pointer concept. In a relational database, columns contain values, not pointers.

Constraints are part of the table's metadata, and serve to make sure the value in the foreign key column does not get out of sync with the key column it references. Either it block changes, or duplicates changes if you declare the foreign key constraint with cascading effects.

Other implementations of RDBMS might have this feature, but not MySQL.