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This article mainly explains "how the PostgreSQL function returns OUT parameters". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn how the PostgreSQL function returns OUT parameters.

1. The field meaning of the system table pg_proc

Prorettype: return value type

Proretset: whether the return value is a collection

Proargmodes: parameter mode (IN, OUT, INOUT)

2. Find ready-made examples

In general, we can find ways to use it in the existing code of PG:

SELECT proname,proargmodes,prorettype::regtype,array_position (proargmodes,'o') FROM pg_proc WHERE NOT proretset AND proargmodes IS NOT NULL AND (array_position (proargmodes,'o') IS NOT NULL OR array_position (proargmodes,'b') IS NOT NULL) LIMIT 10

Returns the function definition that contains the OUT and INOUT parameters, and'b'is the INOUT parameter. Note the use of:: regtype above to enhance the readability of the results:

Pg_stat_get_archiver | {record | 1pg_event_trigger_table_rewrite_oid | {o oid | 1

More results.

3. Return multiple OUT parameters

Open the function pg_stat_get_archiver

/ / define TupleDesc by yourself, the quantity does not include IN input parameter / / same as the construction method of returned result set mentioned earlier tupdesc = CreateTemplateTupleDesc (7); / / different places BlessTupleDesc (tupdesc); / * build values and nulls array * / / return result PG_RETURN_DATUM (HeapTupleGetDatum (tupdesc, values, nulls))

The result set function calls BlessTupleDesc in TupleDescGetAttInMetadata.

4. Return a single output parameter

Call the PG_RETURN_xxx series directly and return it. In the pg_event_trigger_table_rewrite_oid function:

PG_RETURN_OID (currentEventTriggerState- > table_rewrite_oid)

5. INOUT parameters

There are no examples of official code, guess can be like this: the input value is obtained by PG_GETARG_xx, the output is the same as OUT, you can write a code to try if you are interested.

At this point, I believe you have a deeper understanding of "how the PostgreSQL function returns OUT parameters". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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