postgresql return 0 if returned value is null

postgresql, sql

Solution

use coalesce

COALESCE(value [, ...])

The COALESCE function returns the first of its arguments that is not null.  
Null is returned only if all arguments are null. It is often
used to substitute a default value for null values when data is
retrieved for display.

Edit

Here's an example of `COALESCE` with your query:

SELECT AVG( price )
FROM(
      SELECT *, cume_dist() OVER ( ORDER BY price DESC ) FROM web_price_scan
      WHERE listing_Type = 'AARM'
        AND u_kbalikepartnumbers_id = 1000307
        AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
        AND COALESCE( price, 0 ) > ( SELECT AVG( COALESCE( price, 0 ) )* 0.50
                                     FROM ( SELECT *, cume_dist() OVER ( ORDER BY price DESC )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) g
                                    WHERE cume_dist < 0.50
                                  )
        AND COALESCE( price, 0 ) < ( SELECT AVG( COALESCE( price, 0 ) ) *2
                                     FROM( SELECT *, cume_dist() OVER ( ORDER BY price desc )
                                           FROM web_price_scan
                                           WHERE listing_Type='AARM'
                                             AND u_kbalikepartnumbers_id = 1000307
                                             AND ( EXTRACT( DAY FROM ( NOW() - dateEnded ) ) ) * 24 < 48
                                         ) d
                                     WHERE cume_dist < 0.50)
     )s
HAVING COUNT(*) > 5

IMHO `COALESCE` should not be use with `AVG` because it modifies the value. `NULL` means unknown and nothing else. It's not like using it in `SUM`. In this example, if we replace `AVG` by `SUM`, the result is not distorted. Adding 0 to a sum doesn't hurt anyone but calculating an average with 0 for the unknown values, you don't get the real average.

In that case, I would add `price IS NOT NULL` in `WHERE` clause to avoid these unknown values.

Problem

Original source