Question

when i foreign reference a table, is there any point in declaring that column as unique?

I mean of course that column which I’m referencing to is unique.

Answer 1

Yes, picture the following scenario:

Table 1’s id field is your foreign key. It is a unique index.

Table 1:
________________________  
| id |  value | blah... |  
|----|--------|---------|  
| 0  |  val 1 | ....    |  
|----|--------|---------|  
| 1  |  val 2 | ....    |  
|----|--------|---------|  
 ...    ...       ...

Now there are two possibilities with table 2.

1) table_1_id is not unique

Table 2:
_____________________________
| id |  table_1_id | blah... |  
|----|-------------|---------|  
| 0  |      1      | ....    |  <------ Duplicates are okay!
|----|-------------|---------|  <--/
| 1  |      1      | ....    |  
|----|-------------|---------|  
 ...    ...       ...

2) table_1_id is unique

Table 2:
_____________________________
| id |  table_1_id | blah... |  
|----|-------------|---------|  
| 0  |      1      | ....    |  
|----|-------------|---------|  
| 1  |      n      | ....    |  <------- Cannot be 1, no duplicates
|----|-------------|---------|  
 ...    ...       ...