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Friends, I have a quick question for you. Why does SUM of an empty table returns NULL & Not 0 ? Let me just create some sample examples for you.
-- CREATE TABLE testSUMNulls ( ID TINYINT ) GO INSERT INTO testSUMNulls (ID) VALUES (NULL),(NULL),(NULL),(NULL) SELECT SUM(ID) FROM testSUMNulls --
-- CREATE TABLE testSumEmptyTable ( ID TINYINT ) GO SELECT SUM(ID) Sums FROM testSumEmptyTable --
-- CREATE TABLE testSumTable ( ID TINYINT ) GO INSERT INTO testSumTable(ID) VALUES (10),(20),(30),(40) SELECT SUM(ID) Sums FROM testSumTable WHERE ID = 1 --
Now in all the cases we will get NULL as the sum output. Now in all the cases we will get NULL as the sum output. As far as I know SQL internally works with Bags(https://msbiskills.com/2015/09/15/sql-server-what-are-bags-sets/) not sets. Now if our bag doesn’t have anything why we are getting NULL and not 0. Now the question is why it so ?
Please add your answers in the comments section. Enjoy !! We all need to learn.
Pawan Kumar Khowal