Multi-column UNIQUE-ness constraint

Sometimes the each column can have the same value more than once, but 2 (or more column) put together must be unique. For example in this table we are storing coordinates of points. Both x and y can be any value and the same value can appear multiple times in either x or y.

However the (x, y) pair must be unique.

Here is how we can accomplish that.

CREATE TABLE points (
    x INTEGER,
    y INTEGER
);
CREATE UNIQUE INDEX xy_index ON points (x, y);


INSERT INTO points (x, y) VALUES (2, 3);
INSERT INTO points (x, y) VALUES (4, 5);
INSERT INTO points (x, y) VALUES (2, 3);

SELECT * FROM points;

$ sqlite3 < examples/points.sql

Error near line 10: UNIQUE constraint failed: points.x, points.y
2|3
4|5