On 7 Nov 2019, at 20:47, Chris Peachment wrote:
> 1. generate a list of pseudo-random numbers, using a pre-defined
> seed value, over the range 1 .. count(*) of records in table,
>
> 2. use that list as record id values to select the desired subset
> of the data in the table.
>
> This
On 11/7/19 5:13 PM, Doug Currie wrote:
> On Thu, Nov 7, 2019 at 4:23 PM Richard Damon
> wrote:
>
>> One thought would be to generate a ‘hash’ from part of the record, maybe
>> the record ID, and select records based on that value. The simplest would
>> be something like id%100 == 0 would get you
On Thu, Nov 7, 2019 at 4:23 PM Richard Damon
wrote:
>
> One thought would be to generate a ‘hash’ from part of the record, maybe
> the record ID, and select records based on that value. The simplest would
> be something like id%100 == 0 would get you 1% of the records. That
> admittedly isn’t
> On Nov 7, 2019, at 2:15 PM, Merijn Verstraaten wrote:
>
>
>> On 7 Nov 2019, at 19:16, David Raymond wrote:
>>
>> Along those lines SQLite includes the reverse_unordered_selects pragma
>> https://www.sqlite.org/pragma.html#pragma_reverse_unordered_selects
>> which will flip the order it
ge-
From: sqlite-users On Behalf Of
Merijn Verstraaten
Sent: Thursday, November 7, 2019 2:16 PM
To: SQLite mailing list
Subject: Re: [sqlite] Deterministic random sampling via SELECT
> On 7 Nov 2019, at 19:16, David Raymond wrote:
>
> Along those lines SQLite includes the rev
In the very old days before computers were common, a random number
table appeared at the back of many statistical texts. This was used
to select a series of random numbers which would then be used as
look-up indices into some other data set.
You could do the same:
1. generate a list of
>
> Regarding: "So far the only suggestion was "use some non-deterministic
> random sampling method and store the result", but since my samples are
> large and I have lots of them, this would balloon my storage by >100x and I
> don't have the available storage to make that work."
But Keith
> On 7 Nov 2019, at 19:16, David Raymond wrote:
>
> Along those lines SQLite includes the reverse_unordered_selects pragma
> https://www.sqlite.org/pragma.html#pragma_reverse_unordered_selects
> which will flip the order it sends rows in queries that don't explicitly
> specify an ordering.
: [sqlite] Deterministic random sampling via SELECT
On 7 Nov 2019, at 1:56pm, David Raymond wrote:
> Others will correct me if I'm wrong on that.
No correction, but I wanted to add something.
According to the theory of how SQL (not just SQLite, SQL) works, tables have no
order. You
On 7 Nov 2019, at 1:56pm, David Raymond wrote:
> Others will correct me if I'm wrong on that.
No correction, but I wanted to add something.
According to the theory of how SQL (not just SQLite, SQL) works, tables have no
order. You can, in theory, query a table of 100 rows with
SELECT a,b
On Thursday, 7 November, 2019 04:55, Merijn Verstraaten
wrote:
>I'm trying sample a (deterministically) random subset of a SELECT query,
You cannot have something that is both RANDOM and DETERMINISTIC at the same
time.
>the most common solution on the internet to get random samples seems to
"So, is this behaviour documented/guaranteed somewhere?"
Short version is: Nope. The engine is free to do whatever it wants as long as
it gives the correct result in the end.
Consider a simple
select * from foo where predicate order by non_indexed_field;
Since there is no nice ordering of the
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