MySQL multiple records judgment add minus to calculate

Code pay Payflag
00001 100.00 0
00001 50.00 1
00001 50.00 0
00002 200.00 0

Pay is Decimal,payflag 0 is Payment, 1 is a refund
Add the same code and payflag=0 pay minus payflag=1 pay to get the following data

Code pay
00001 100.00
00002 200.00

The first type:

Select Code,sum (pay* (case Payflag, 1 then-1 else 1 end)) as pay
from [table]
Group BY Code

The second type:

Select Code,sum (if (payflag=0,pay,-1*pay))
From TT

Group BY Code

Third Kind

SUM (Pay* (cos (PI () as Pay [tablename] bycode     

MySQL multiple records judgment add minus to calculate