On Mon, Dec 8, 2014 at 4:55 AM, Gwendal Roué <g...@pierlis.com> wrote:
> Hi, > > Unique indexes make some valid update queries fail. > > Please find below the SQL queries that lead to the unexpected error: > > -- The `books` and `pages` tables implement a book with several pages. > -- Page ordering is implemented via the `position` column in the pages > table. > -- A unique index makes sure two pages do not share the same position. > CREATE TABLE books ( > id INT PRIMARY KEY > ) > CREATE TABLE pages ( > book_id INT NOT NULL REFERENCES books(id) ON DELETE CASCADE ON > UPDATE CASCADE, > position INT > ) > CREATE UNIQUE INDEX pagination ON pages(book_id, position) > > -- Let's populate the tables with a single book and three pages: > INSERT INTO books VALUES (0); > INSERT INTO pages VALUES (0,0); > INSERT INTO pages VALUES (0,1); > INSERT INTO pages VALUES (0,2); > > -- We want to insert a page between the pages at positions 0 and 1. So we > have > -- to increment the positions of all pages after page 1. > -- Unfortunately, this query yields an error: "columns book_id, position > are not unique"/ > > UPDATE pages SET position = position + 1 WHERE book_id = 0 AND position >= > 1; > > The query should run without any error, since it does not break the unique > index. > Uniqueness is checked for each row change, not just at the end of the transaction. Hence, uniqueness might fail, depending on the order in which the individual rows are updated. > > Thank you for considering this issue. > > Cheers, > Gwendal Roué > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
