“Insert if not exists” statement in SQLite

Question

I have an SQLite database. I am trying to insert values (users_id, lessoninfo_id) in table bookmarks, only if both do not exist before

Answer 1

If you never want to have duplicates, you should declare this as a table constraint:

CREATE TABLE bookmarks(
    users_id INTEGER,
    lessoninfo_id INTEGER,
    UNIQUE(users_id, lessoninfo_id)
);

(A primary key over both columns would have the same effect.)

It is then possible to tell the database that you want to silently ignore records that would violate such a constraint:

INSERT OR IGNORE INTO bookmarks(users_id, lessoninfo_id) VALUES(123, 456)

Answer 2

insert into bookmarks (users_id, lessoninfo_id)

select 1, 167
EXCEPT
select user_id, lessoninfo_id
from bookmarks
where user_id=1
and lessoninfo_id=167;

This is the fastest way.

For some other SQL engines, you can use a Dummy table containing 1 record. e.g:

select 1, 167 from ONE_RECORD_DUMMY_TABLE

Answer 3

For a unique column, use this:

INSERT OR REPLACE INTO table () values();

For more information, see: sqlite.org/lang_insert

Answer 4

If you have a table called memos that has two columns id and text you should be able to do like this:

INSERT INTO memos(id,text) 
SELECT 5, 'text to insert' 
WHERE NOT EXISTS(SELECT 1 FROM memos WHERE id = 5 AND text = 'text to insert');

If a record already contains a row where text is equal to 'text to insert' and id is equal to 5, then the insert operation will be ignored.

I don't know if this will work for your particular query, but perhaps it give you a hint on how to proceed.

I would advice that you instead design your table so that no duplicates are allowed as explained in @CLs answer below.