如果返回的值为null，则PostgreSQL返回0

小编典典

如果返回的值为null，则PostgreSQL返回0

sql

我有一个查询返回avg（price）

  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 price>( select avg(price)* 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 price<( select avg(price)*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

如果没有可用值，如何使它返回0？

阅读 260

2021-04-15

共1个答案

小编典典

使用合并

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.

编辑

这是COALESCE查询的示例：

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

IMHOCOALESCE不应与之一起使用，AVG因为它会修改值。NULL意味着未知，别无其他。这不像是在中使用它SUM。在此示例中，如果我们替换AVG为SUM，则结果不会失真。将总和加0不会对任何人造成伤害，但是对于未知值计算平均值为0时，您不会获得真实的平均值。

在那种情况下，我将添加price IS NOT NULLinWHERE子句以避免这些未知值。

2021-04-15