$ sqlite3
SQLite version 3.6.23.1
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> CREATE TABLE Foo(a INTEGER, b INTEGER, UNIQUE (a, b));
sqlite> INSERT INTO Foo VALUES (1, 2);
sqlite> INSERT INTO Foo VALUES (1, 3);
sqlite> INSERT INTO Foo VALUES (2, 2);
sqlite> INSERT INTO Foo VALUES (2, 2);
Error: columns a, b are not unique