Question

I’m trying to create a parametric query that will be executed in a loop using plpgsql.

The 2 parameters will be the starting latitude/longitude points passed into the query. The latitude and longitude points will be retrieved from an array – so it will be a foreach like iteration over the array and to pass the two lat/lon values into the query for every execution.

How would I do something like this?

My query and the implementation way I thought is like the following: (the X,Z values are the parametric latitude/longitude values that will be passed, Y and T will be obtained by performing a certain calculation that I will handle). For clarity, my query returns multi-row and multi-columned results (timestamp and count) since it counts and returns the number of requests that fall into hour intervals(timestamps)

for each latitude-longitude pair X,Z in array

find Y and T from X and Z

WITH cal AS (
    SELECT generate_series('2011-02-02 00:00:00'::timestamp ,
                           '2012-04-01 05:00:00'::timestamp , 
                           '1 hour'::interval) AS stamp
),
qqq AS (
  SELECT date_trunc('hour', calltime) AS stamp, count(*) AS zcount
  FROM mytable
  WHERE calltime >= '2011-02-13 22:55:11' 
    AND calltime <= '2012-02-13 01:02:21'
    AND (calltime::time >= '22:55:11' 
    OR calltime::time <= '01:02:21')
    AND lat >= X 
    AND lat <= Y
    AND lon >= Z
    AND lon <= T
 GROUP BY date_trunc('hour', calltime)
)
SELECT cal.stamp, COALESCE (qqq.zcount, 0) AS zcount
FROM cal
LEFT JOIN qqq ON cal.stamp = qqq.stamp
WHERE cal.stamp >= '2011-02-13 22:00:00' 
  AND cal.stamp <= '2012-02-13 01:02:21' 
  AND (
    extract ('hour' from cal.stamp) >= extract ('hour' from '2011-02-13 22:00:00'::timestamp) or
    extract ('hour' from cal.stamp) <= extract ('hour' from '2012-02-13 01:02:21'::timestamp) 
  )
ORDER BY stamp ASC;

Answer 1

• Pass an array into the function and FOR r IN SELECT * FROM unnest(the_array) LOOP over the elements in the array, where r is a record variable that’s in the DECLARE clause of the function; or

• Loop over a refcursor passed into the function. See PL/PgSQL cursors.

Even better, avoid the LOOP and integrate the SELECT unnest(thearray) into your CTE. Loops in PL/PgSQL are much slower than the equivalent in a SQL CTE is likely to be.

See unnest, LOOP.