Re: Need help requiring uniqueness in text columns

Hello

IDEA 3:

Use two hash functions:

CREATE UNIQUE INDEX uidx ON TEST((decode(md5(a),'hex')),(hashtext(a)));

removing spaces helps
CREATE UNIQUE INDEX uidx ON test((decode(md5(lower(replace(a,' ',''))),'hex')));

Regards
Pavel Stehule

CREATE UNIQUE INDEX nodups on MESSAGE (my_timestamp_col, md5(my_text_col));
>

On 02/01/2008, Matthew Wilson <matt(at)tplus1(dot)com> wrote:
> I have a table MESSAGE with a text column and a timestamp column. I
> want to make sure that I have no rows with duplicates for both values.
> I have two ideas right now for how to do this.
>
> IDEA 1:
>
> CREATE UNIQUE INDEX nodups on MESSAGE (my_timestamp_col, my_text_col);
>
> IDEA 2:
>
> CREATE UNIQUE INDEX nodups on MESSAGE (my_timestamp_col, md5(my_text_col));
>
> I am speculating that an index on the md5 is cheaper than on a text
> column. I'm willing to risk the chance of a hash collision.
>
> I don't want to use this index to allow searching inside the text
> column. I just want to protect against duplication.
>
> Are either of these approaches any good? What are other ways to
> guarantee uniqueness for the pair of my timestamp column and my text
> column?
>
> TIA
>
> Matt
>
>
> --
> Programming, economics, gardening, life in Cleveland.
> http://blog.tplus1.com
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
> choose an index scan if your joining column's datatypes do not
> match
>