Re: Row ordering after CREATE TABLE AS...SELECT regexp_split_to_table(source_text, regexp) AS new_column

John Gage <jsmgage(at)numericable(dot)fr> writes:
> This is a two-part question:
> 1) I have a source_text that I want to divide into smaller subunits
> that will be contained in rows in a column in a new table. Is it
> absolutely certain that the initial order of the rows in the resultant
> table after this operation:

> CREATE TABLE new_table AS SELECT regexp_split_to_table(source_text,
> E'regexp') as subunits FROM source_table;

> will be the same as the order of these subunits in the original text?

If you have a version new enough to have synchronize_seqscans, you'd
need to turn that off. Otherwise should be OK.

> 2) I would like to be able to create a serial-type column during
> CREATE TABLE AS in the new table that "memorizes" this order so that I
> can reconstruct the original text using ORDER BY on that serial
> column. However, I am stumped how to do that.

I think the trick is to get the SRF to be expanded before the serial
values are assigned. There's more than one way to do it, but I think
(too tired to experiment) this would work:

CREATE TABLE new_table (id serial, subunits text);

INSERT INTO new_table(subunits) SELECT regexp_split_to_table(source_text,
E'regexp') FROM source_table;

regards, tom lane