Question

I’m using sqlite in android app and I want to make insert in table by 2 unique row values. For example:

id| column1 | column2 | column3|
1.   1              2     3  
2.   2              3     4

Unique columns – COLUMN1 and COLUMN2

 INSERT OR REPLACE INTO HISTORY (id, column1, column2, column3) VALUES (null, 2, 3, 6);

But this query shouldn’t works ’cause 1st and 2nd values isn’t unique in table

Thnx.

Answer 1

If I understand your question, simply use the UNIQUE constraint when building your table:

CREATE TABLE History (
    _id INTEGER PRIMARY KEY,
    column1 INTEGER,
    column2 INTEGER,
    column3 INTEGER,
    UNIQUE (column1, column2));

Then if you try these INSERT statements:

INSERT INTO History (column1, column2, column3) VALUES (2, 3, 0);
INSERT INTO History (column1, column2, column3) VALUES (2, 3, 6);

The second will fail because column1 and column2 already exist.

Understand that if you use INSERT OR REPLACE in my example, the second statement will replace the first (no exception thrown).

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but how can i add unique to existed table?

Typically you would use ALTER TABLE to add a constraint to your existing tables, but SQLite does not allow this… However you can workaround this limitation:

CREATE UNIQUE INDEX name ON History(column1, column2);