sql create table with condition that 2 columns cannot have equal values

Question

How can I write a condition in a create table statement to say 2 columns cannot be equal?

CREATE table Example(
    sendId integer,
    recieveId integer,
    **!sendId cannot equal recieveId**

);

Answer 1

Use a check constraint:

CREATE table Example(
    sendId integer,
    recieveId integer,
    constraint not_equal check (sendid <> recieveId)
);

As your columns allow null values, you might want to take care of that too:

CREATE table Example(
    sendId integer,
    recieveId integer,
    constraint not_equal check (coalesce(sendid,0) <> coalesce(recieveId,0))
);

That treats NULL as 0 maybe using a different value that could never occur might be more appropriate.

Depending on your DBMS product, you could also use the standard operator is distinct from

constraint not_equal check (sendid is distinct from receiveid)

Answer 2

You would use a check constraint:

create table Example (
    sendId integer,
    receiveId integer,
    constraint chk_example_sendId_receiveId check (sendId <> receiveId)
);

Answer 3

You need check constraint :

constraint chk_sendId_receiveId check (sendId <> receiveId)