On 11/06/2016 05:12 PM, Emrul wrote:
Hi,
I have a function that returns an SQL string as follows:
CREATE OR REPLACE FUNCTION t1() RETURNS text AS
$$
BEGIN
RETURN 'SELECT * FROM mytable';
END
$$ LANGUAGE plpgsql;
and I want to create a second function (t2) that will execute the string
returned by t1() and return the results. I thought about using RETURN QUERY
EXECUTE as documented here:
https://www.postgresql.org/docs/9.6/static/plpgsql-control-structures.html
but there's a note towards the end that says '/if a PL/pgSQL function
produces a very large result set, performance might be poor: data will be
written to disk to avoid memory exhaustion, but the function itself will not
return until the entire result set has been generated./'
Is there any other way I can achieve execution of the dynamic SQL from t1()
without having the whole result set retrieved inside the function itself?
https://www.postgresql.org/docs/9.5/static/plpgsql-cursors.html
"Rather than executing a whole query at once, it is possible to set up a
cursor that encapsulates the query, and then read the query result a few
rows at a time. One reason for doing this is to avoid memory overrun
when the result contains a large number of rows. (However, PL/pgSQL
users do not normally need to worry about that, since FOR loops
automatically use a cursor internally to avoid memory problems.) A more
interesting usage is to return a reference to a cursor that a function
has created, allowing the caller to read the rows. This provides an
efficient way to return large row sets from functions."
note: My example above is simplified, my real t1() function takes some
parameters and generates SQL depending upon those parameters.
Thanks!
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Adrian Klaver
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