Question

I would like to design a table named arguments whose an attribute name is linked to another attribute name in a table called names.

I see two ways to express it in SQL:

1. by creating a constraint on the table:

   CREATE TABLE names (   name text UNIQUE,
                         short text UNIQUE,
                       comment text);
   CREATE TABLE arguments (   name text UNIQUE,
                           comment text,
                           FOREIGN KEY (name) REFERENCES names (name));
   

2. by qualifying the attribute on-the-fly:

   CREATE TABLE names (   name text UNIQUE,
                         short text UNIQUE,
                       comment text);
   CREATE TABLE arguments (   name text UNIQUE REFERENCES names (name),
                           comment text);
   

I would like to know:

• if one of the two is commonly known as better than the other, and
• if it can have consequences that I should be aware of.

Thank you for your help.

Answer 1

While the first option is known as out-of-line constraint declaration and the second option is in-line, both of them are functionally same.

What would be better is to assign a name to the foreign key constraint. If you have a name, you can selectively enable and disable the constraint if required.

Create table

CREATE TABLE arguments 
(   
    name text UNIQUE,                         
    comment text,                         
    constraint arguments_fk FOREIGN KEY (name) REFERENCES names (name)
); 

Disable constraint

ALTER TABLE arguments NOCHECK CONSTRAINT arguments_fk;

Enable constraint

ALTER TABLE arguments CHECK CONSTRAINT arguments_fk;

This is for SQL Server. Oracle has equivalent commands.