I am looking for a way to combine two tables with the same fields in a way that the devicename which is common between the two gets added

See below example

2 tables a and b, with identical columns, I want to union them, so one column is device name other is error count, if I use union, will the count column be summed itself, or we have to do something else, i.e.

T1

devicename error count

a 10

b 12

c 15

T2

devicename error count

b 77

c 88

d 99

e 15

f 19

union T1, T2

Current result

a 10

b 12

c 15

b 77

c 88

d 99

e 15

f 19

Intended result

a 10

b 89

c 103

d 99

e 15

f 19

Please let me know if I need to use some other method for the intended results.