[odb-users] Native query error

Boris Kolpackov boris at codesynthesis.com
Fri Sep 6 07:38:29 EDT 2013

Hi Gunjur,

Gunjur Munireddy Prashanth / LOKISA Smart Energy GmbH <GPrashanth at prosolartec.de> writes:

> I am using native sql query to get the average of a column and I get
> the average has  1.0000
> float avg = db->execute("SELECT AVG(mod_il2) FROM OddDay");

For SELECT the database::execute() function returns the number of
rows selected. You are expecting it to return the first column from
the first row.

To handle a query like this with ODB you will need to use a view.
For example:

#pragma db view query("SELECT AVG(mod_il2) FROM OddDay")
struct OddDay_mod_il2_avg
  float value;

float avg = db->query<OddDay_mod_il2_avg> ().begin ()->value;

For more information on views, see Chapter 9, "Views" in the ODB Manual.


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