Question

I have table A and there is a column name COL_A.

I want that if someone change the value, lets say from 1 to 'X' (not costant) that the trigger will change it back from 'X' to 1.

Answer 1

SQLite does not support changing the new column values.
The only way to change a column in a trigger would be to run an UPDATE command,
but that would run the trigger again.

What you can do is to prevent changing the column in the first place:

CREATE TRIGGER IF NOT EXISTS prevent_col_a_change
BEFORE UPDATE OF col_a ON a
BEGIN
    SELECT RAISE(ABORT, 'COL_A must not be changed');
END;