Question

我正在使用以下查询，如果sum(otb.special_discount)的结果不为空，则该查询正常工作。但如果结果为null，则sum查询的整个结果将返回null。

我应该如何更正例如sum(otb.total_charges)的查询为10000且sum(otb.special_discount)为空，我希望结果为10000。

SELECT ott.test_name, (sum(otb.total_charges)- sum(otb.special_discount))as test_charges,
count(otb.id)count
from opd_test_bill otb,opd_test_type ott where otb.bill_type='p'
and otb.test_name=ott.id 
and date between '2015-04-26 16:00:59' and '2015-04-27 06:00:00' 
group by ott.test_name

Answer 1

快速解决方案：

SELECT ott.test_name, (COALESCE(sum(otb.total_charges),0)- COALESCE(sum(otb.special_discount),0))as test_charges,
count(otb.id)count
from opd_test_bill otb,opd_test_type ott where otb.bill_type='p'
and otb.test_name=ott.id 
and date between '2015-04-26 16:00:59' and '2015-04-27 06:00:00' 
group by ott.test_name

https://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#function_coalesce

返回列表中的第一个非NULL值，如果没有非NULL值，则返回NULL。

您也可以使用＆＃39; IFNULL＆＃39;：

https://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html#function_ifnull

SELECT ott.test_name, (IFNULL(sum(otb.total_charges),0)- IFNULL(sum(otb.special_discount),0))as test_charges,
count(otb.id)count
from opd_test_bill otb,opd_test_type ott where otb.bill_type='p'
and otb.test_name=ott.id 
and date between '2015-04-26 16:00:59' and '2015-04-27 06:00:00' 
group by ott.test_name

Answer 2

使用COALESCE功能：

     SELECT ott.test_name, 
     (sum(otb.total_charges)- COALESCE(sum(otb.special_discount),0))as test_charges,
     count(otb.id)count
     from opd_test_bill otb join opd_test_type ott 
     on otb.test_name=ott.id     
     where otb.bill_type='p'and date between '2015-04-26 16:00:59' and '2015-04-27 06:00:00' 
      group by ott.test_name

mysql sum其中sum结果为Null

2 个答案: