Question

I amy trying to build a statistics table for marketing issues for specific site :

currently I planning to build table like this

Source_IP    source_city    Destination_IP   destination_city 
127.0.0.1       NY           242.212.12.1         Paris
242.212.12.1   Paris           127.0.0.1           NY  

I want to prevent case like the above I.E the combination of (Source_ip , source_city) and (Destination_IP destination_city) should only be one record and not 2 how can i prevent this on sql?

Answer 1

Assuming your DBMS allows function based indexes, the following would do the trick:

CREATE UNIQUE INDEX idx_no_dupes 
    ON your_table (least(source_ip, destination_ip), greatest(source_ip, destination_ip));

The use of least and greatest will always index the tuples in the “same order”, so it doesn’t matter which value is in which column.

If your DBMS does not support least or greatest you will need to replace this with a CASE construct.