Re: Indexing fragments of a column's value ?

On Fri, Nov 3, 2023 at 3:34 PM David Gauthier <dfgpostgres(at)gmail(dot)com> wrote:

> I'm asking about the possibility of indexing portions of a column's value
> where the column has a static field format. Example, a char(8) which
> contains all hex values (basically a hex number that's always 8 chars wide,
> leading zeros if needed). Someone might want to select all recs where the
> first 2 digits are 'ff' or maybe the last 4 hex digits match regexp_match
> '00[cdef]{2}' or maybe a match of the entire string... "0dd63a87".
>
> If I know the placement and width of the fields that need to be indexed,
> can indices be defined to facilitate queries ? Example...
> - match all 8 chars
> - match the 3rd and 4th chars
> - match the last 4 chars
>
> I suppose I could fragment the thing into multiple columns for the
> purposes of a search. So add a column called "last4" as a char(4) that
> matches the last 4 chars of that column. Then index that. etc... But
> inquiring to see if there is something more elegant.
>
> Just curious why not store it as a HEX string (functional index, even).
And allow searching against the stringified hex, then your regex works?

Kirk