add THREE table A&B&C coloums

Question

i have table like

 

table_A

sno     item    amount

1         asdf      545.00

 

table_b

sno    item     amount

1        dfgh      876

 

table_c

sno    item    amount

 

 

 i have o/p like

i want csharp code read  table_A, table_b ,table_c  item  , amount and add two tables A&b&c  ...

if table_c  is null or empty it not considered

 

 

o/p like

asdf    545

dfgh    876

total   1421