CODEWITHSUNDEEP
sqlpostgresqlplr
Dave Jarvis
Dave Jarvis

Reputation: 31191

Return query results into an array

The following code snippet creates three arrays, which are passed into a PL/R function.

FOR s_id, s_latitude, s_longitude IN 
  SELECT
    s.id,
    s.latitude_decimal,
    s.longitude_decimal
  FROM
    climate.station s
  WHERE
    s.applicable AND
    s.latitude_decimal BETWEEN box.latitude_min AND box.latitude_max AND
    s.longitude_decimal BETWEEN box.longitude_min AND box.longitude_max
LOOP
  SELECT array_append( v_id, s_id ) INTO v_id;
  SELECT array_append( v_latitude, s_latitude ) INTO v_latitude;
  SELECT array_append( v_longitude, s_longitude ) INTO v_longitude;
END LOOP;

The arrays are declared as:

  v_id integer[];
  v_latitude double precision[];
  v_longitude double precision[];

I would rather use CREATE TYPE and pass one array with each element containing three values.

How would you code this so that it does not use a FOR ... LOOP?

The first line of the PL/R function is:

stations <- cbind( v_id, v_longitude, v_latitude )

I would like to eliminate that line of code and simplify the SELECT query.

Thank you.

Upvotes: 2

Views: 944

Answers (2)

rfusca
rfusca

Reputation: 7705

According to the pl/r documentation, "...two-dimensional PostgreSQL arrays are mapped to R matrixes..."

Maybe something like...

  SELECT
    plr_function(
      array_agg(array[s.id,s.latitude_decimal,s.longitude_decimal])
    )
  FROM
    climate.station s
  WHERE
    s.applicable AND
    s.latitude_decimal BETWEEN box.latitude_min AND box.latitude_max AND
    s.longitude_decimal BETWEEN box.longitude_min AND box.longitude_max

Upvotes: 1

Diogo Biazus
Diogo Biazus

Reputation: 622

You could use the following code and continue using 3 arrays:

SELECT
  array_agg(s.id),
  array_agg(s.latitude_decimal),
  array_agg(s.longitude_decimal)
INTO
  v_id, v_latitude, v_longitude
FROM
  climate.station s
WHERE
  s.applicable AND
  s.latitude_decimal BETWEEN box.latitude_min AND box.latitude_max AND
  s.longitude_decimal BETWEEN box.longitude_min AND box.longitude_max

or use the row constructor and assemble an array of a composite type:

SELECT
  array_agg((
    s.id,
    s.latitude_decimal,
    s.longitude_decimal
  ))
INTO
  v_id, v_latitude, v_longitude
FROM
  climate.station s
WHERE
  s.applicable AND
  s.latitude_decimal BETWEEN box.latitude_min AND box.latitude_max AND
  s.longitude_decimal BETWEEN box.longitude_min AND box.longitude_max

BTW, this will only work on PostgreSQL 8.4+

Upvotes: 1

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