Re: create a temp table in SPI

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