On Wed, Sep 9, 2026 at 6:33 PM Igor Korot <[email protected]> wrote:
> Hi, > > On Wed, Sep 9, 2026 at 5:23 PM Ron Johnson <[email protected]> > wrote: > > > > On Wed, Sep 9, 2026 at 1:43 PM Igor Korot <[email protected]> wrote: > >> > >> Hi, ALL, > >> Can below 4 queries > >> > >> std::wstring query1 = L"SELECT rolname FROM pg_roles"; > >> std::wstring query2 = L"SELECT datname FROM pg_database WHERE > >> datistemplate = true;"; > >> std::wstring query3 = L"SELECT pg_encoding_to_char( conforencoding > >> ) AS name FROM pg_conversion"; > >> std::wstring query4 = L"SELECT collname, collencoding, > >> collprovider collctype FROM pg_collation"; > >> std::wstring query5 = L"SELECT spcname FROM pg_tablespace"; > >> > >> be made as one big query to use a 1 DB hit? > > > > > > Bereft of the C++ cruft, here are the queries: > > SELECT rolname > > FROM pg_roles; > > > > SELECT datname > > FROM pg_database > > WHERE datistemplate = true; > > > > SELECT pg_encoding_to_char(conforencoding) AS name > > FROM pg_conversion; > > > > SELECT collname, collencoding, collprovider, collctype > > FROM pg_collation; > > > > SELECT spcname > > FROM pg_tablespace; > > > > The sticky wicket is the four columns in the pg_collation query. > > > > You could probably write a stored function or procedure which returns a > complex json object with the results of the four queries (or four jsonb > objects, one for each query). You'd of course have to decode the json in > your C++ program. > > > > Without the pg_collation query, you could make a UNION ALL like: > > SELECT 'pg_roles' AS table_name, rolname::text AS row_value > > FROM pg_roles > > UNION ALL > > SELECT 'pg_database' AS table_name, datname ::text AS row_value > > FROM pg_database > > WHERE datistemplate = true > > UNION ALL > > SELECT ' pg_conversion' AS table_name > > , pg_encoding_to_char(conforencoding)::text AS row_value > > FROM pg_conversion > > UNION ALL > > SELECT pg_tablespace AS table_name, spcname ::text AS row_value > > FROM pg_tablespace; > > > > It's a lot of complication, though, for something which shouldn't be > called very often. > > I was hoping to have some kind of join query. ;-) > But you are right - the UNION ALL doesn't make sense for a > "1-in-a-lifetime" query. > I could probably FULL OUTER JOIN them on the oid column. I don't know how many rows are pg_collation, but if there are a lot, you're going to be returning a whole lot of rows with null values, and application logic must do something like "if *this* column is not null, then it's a role; if *that* column is not null, then it's a database; etc etc". KISS and make four queries... -- Death to <Redacted>, and butter sauce. Don't boil me, I'm still alive. <Redacted> lobster!
