[GENERAL] select null + 0 question

[Jean-Christian Imbeault]

Why is it that "select null + 1" gives null but "select sum(a) from 
table" where there are null entries returns an integer?

Shouldn't the sum() and "+" operators behave the same?

TAL=# select null + 0;
 ?column?
----------
(1 row)

TAL=# select * from a;
 a
---
 1
(3 rows)
TAL=# select sum(a) from a;
 sum
-----
   1
(1 row)
Thanks,

Jean-Christian Imbeault

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