PHP / MYSQL：如果记录尚未在数据库中，则值为0

I have the following query:

$query = "SELECT (SELECT SUM(net_amount) FROM fin_costos WHERE month='1' AND group_of_costos='general' AND year_analysis='2014' ) + 
(SELECT SUM(net_amount) FROM em2_fin_costs WHERE month='1' AND group_of_costos='general' AND year_analysis='2014') AS total";

It's basically a SUM of 2 values retrieved from different tables. The problem appears when in one of the SELECT statements, the record is not yet in the database and creates a NULL, that even if the second SELECT gets a value, creates a NULL.

The question: How can I turn to 0 the result from the SELECT statements if the record is not yet on the database.

Use IFNULL():

SELECT IFNULL((SELECT SUM(net_amount) FROM fin_costos WHERE month='1' AND group_of_costos='general' AND year_analysis='2014' ), 0) + 
IFNULL((SELECT SUM(net_amount) FROM em2_fin_costs WHERE month='1' AND group_of_costos='general' AND year_analysis='2014'), 0) AS total

try This

$query = "SELECT (SELECT SUM(case when net_amount IS NOT NULL then net_amount else 0 end) FROM fin_costos WHERE month='1' AND group_of_costos='general' AND year_analysis='2014' ) + (SELECT SUM(case when net_amount IS NOT NULL then net_amount else 0 end) FROM em2_fin_costs WHERE month='1' AND group_of_costos='general' AND year_analysis='2014') AS total";