how to set unique constraint over multiple column when any one can be null in sqlite

Question

How do I set unique constraint over multiple column when any one can be null in sqlite?

e.g. I have made unique(\"col1\",\"col2\",\"col3\") and tried with inse

Answer 1

Starting with version 3.9.0 (2015-10-14) you can use indexes on expressions (https://www.sqlite.org/expridx.html) and use for example the COALESCE function to transform null values into some form of fallback value:

CREATE UNIQUE INDEX IX_Unique ON Table1 (
    COALESCE(col1, ""), 
    COALESCE(col2, ""), 
    COALESCE(col3, "")
);