Re: create a temp table in SPI

Thanks for your explanation.

Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> 于2023年7月13日周四 17:48写道：

> On Thu, 2023-07-13 at 13:12 +0800, 黄宁 wrote:
> > I want to create some temporary tables in SPI, but after I created the
> table and inserted the data, I can’t query any data, why?
> >
> > the postgres version:
> > PostgreSQL 13.6 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 7.3.0,
> 64-bit
> > code:
> >
> >
> > int ret = 0;
> > SPI_connect();
> > ret = SPI_execute("CREATE GLOBAL TEMP TABLE temp_table (id int,
> value text)", false, 0);
> >
> > ret = SPI_execute("INSERT INTO temp_table VALUES (1, 'a'), (2,
> 'b')", false, 0);
> >
> > ret = SPI_execute("SELECT * FROM temp_table", true, 0);
> >
> > if(SPI_processed > 0)
> ...
>
> That's because you set "read_only" to "true" when you executed the query,
> so that the command counter is not incremented, and the query cannot see
> the results from the previous statement.
>
> The documentation is quite clear here:
>
> It is generally unwise to mix read-only and read-write commands within
> a single function using SPI; that could result in very confusing
> behavior,
> since the read-only queries would not see the results of any database
> updates done by the read-write queries.
>
> Yours,
> Laurenz Albe
>