반환 된 값이 null 인 경우 postgresql은 0을 반환합니다.
avg (price)를 반환하는 쿼리가 있습니다.
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
값을 사용할 수없는 경우 0을 반환하는 방법은 무엇입니까?
합체 사용
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.
편집하다
다음 COALESCE은 쿼리 의 예입니다 .
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 COALESCE는 AVG값을 수정하므로 와 함께 사용하면 안됩니다 . NULL알려지지 않은 것을 의미합니다. 에서 사용하는 것과는 다릅니다 SUM. 우리가 바꿀 경우이 예에서, AVG에 의해 SUM, 결과는 왜곡되지 않습니다. 합계에 0을 더하는 것은 누구에게도 해를 끼치 지 않지만 알 수없는 값에 대해 0으로 평균을 계산하면 실제 평균을 얻지 못합니다.
이 경우, 나는 추가 할 수 price IS NOT NULL에서 WHERE이러한 알 수없는 값을 방지하기 위해 절.
(this answer was added to provide shorter and more generic examples to the question - without including all the case-specific details in the original question).
There are two distinct "problems" here, the first is if a table or subquery has no rows, the second is if there are NULL values in the query.
For all versions I've tested, postgres and mysql will ignore all NULL values when averaging, and it will return NULL if there are nothing to average over. This generally makes sense, as NULL is to be considered "unknown". If you want to override this you can use coalesce (as suggested by Luc M).
$ create table foo (bar int);
CREATE TABLE
$ select avg(bar) from foo;
avg
-----
(1 row)
$ select coalesce(avg(bar), 0) from foo;
coalesce
----------
0
(1 row)
$ insert into foo values (3);
INSERT 0 1
$ insert into foo values (9);
INSERT 0 1
$ insert into foo values (NULL);
INSERT 0 1
$ select coalesce(avg(bar), 0) from foo;
coalesce
--------------------
6.0000000000000000
(1 row)
of course, "from foo" can be replaced by "from (... any complicated logic here ...) as foo"
Now, should the NULL row in the table be counted as 0? Then coalesce has to be used inside the avg call.
$ select coalesce(avg(coalesce(bar, 0)), 0) from foo;
coalesce
--------------------
4.0000000000000000
(1 row)
I can think of 2 ways to achieve this:
IFNULL():
The IFNULL() function returns a specified value if the expression is NULL.If the expression is NOT NULL, this function returns the expression.
Syntax:
IFNULL(expression, alt_value)
Example of IFNULL() 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 IFNULL( price, 0 ) > ( SELECT AVG( IFNULL( 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 IFNULL( price, 0 ) < ( SELECT AVG( IFNULL( 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
COALESCE()
The COALESCE() function returns the first non-null value in a list.
Syntax:
COALESCE(val1, val2, ...., val_n)
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
참고URL : https://stackoverflow.com/questions/11007009/postgresql-return-0-if-returned-value-is-null
'Programing' 카테고리의 다른 글
| 네이티브 개체와 호스트 개체의 차이점은 무엇입니까? (0) | 2020.09.18 |
|---|---|
| 스레드에서 값 반환 (0) | 2020.09.18 |
| Emacs를 다시 시작하지 않고 구성 다시로드 (0) | 2020.09.18 |
| System.ComponentModel 기본값 속성 내에서 DateTime 속성의 기본값을 DateTime.Now로 설정 (0) | 2020.09.18 |
| Android singleTask 또는 singleInstance 시작 모드? (0) | 2020.09.18 |