Question

I have a table mytable where is the 2 unique int field

# SQLAlchemy example
mytable = Table('mytable', meta,

# per-column anonymous unique constraint
Column('col1', Integer, unique=True),
Column('col2', Integer, unique=True),

# explicit/composite unique constraint.  'name' is optional.
UniqueConstraint('col1', 'col2', name='uix_1')
)

How to do restrictions like this:

col1 col2
1      
2     6
3     1
4     5
5
6     1 -- FAIL: becouse 3-1 is exist and 2-6 is exist!!!

unique((col1, col2) union (col2, col1))

Answer 1

You can use something like this as a constraint:

create table example (
    col1 integer,
    col2 integer,
    CHECK (col1 < col2),
    UNIQUE(col1, col2)
);

If you want it to automatically make the col1 smaller than col2, use a trigger 🙂