SQLite: Preventing Duplicate Rows

Question

CREATE TABLE Permission ( 
    permissionID INTEGER PRIMARY KEY UNIQUE,
    user         INTEGER
    location     INTEGER 
);

I don\'t want to have

Answer 1

First option is creating a unique constraint on user and location columns which will avoid duplicates.

Create unique index permission_user_location  on permission (user,location);

Else if you already have duplicate rows in table you need to delete the duplicate rows and create unique constraint

To remove duplicate rows use this query

DELETE
FROM Permission 
WHERE NOT EXISTS 
(
select 1 from 
(
select min(permissionID) as permissionID, user, location
From Permission A
Group by user, location
) B
Where B.permissionID = Permission.permissionID
AND   B.user = Permission.User
AND   B.location = Permission.location 
)

Answer 2

CREATE TABLE Permission ( 
    permissionID INTEGER PRIMARY KEY UNIQUE,
    user         INTEGER,
    location     INTEGER 
);
CREATE UNIQUE INDEX user_location ON Permission (user,location);

Answer 3

Declare a unique constraint on (user, location).

CREATE TABLE Permission (
    permissionID integer primary key,
    user integer not null,
    location integer not null,
    unique (user, location)
);

sqlite> insert into Permission (user, location) values (1, 2);
sqlite> insert into Permission (user, location) values (1, 2);
Error: UNIQUE constraint failed: Permission.user, Permission.location