[MonetDB-users] SUM of NULLs is 0?
Dear MonetDB-users, a complete newbie to MonetDB, I can't really tell whether it is a bug, feature or I'm just getting it all wrong. A script below illustrates some weird NULL handling behaviour found in Nov2008-SP2: -- years under audit CREATE TABLE BUDGET_PERIOD (BP smallint NOT NULL); INSERT INTO BUDGET_PERIOD VALUES (1998); INSERT INTO BUDGET_PERIOD VALUES (1999); INSERT INTO BUDGET_PERIOD VALUES (2000); INSERT INTO BUDGET_PERIOD VALUES (2001); INSERT INTO BUDGET_PERIOD VALUES (2002); INSERT INTO BUDGET_PERIOD VALUES (2003); INSERT INTO BUDGET_PERIOD VALUES (2004); INSERT INTO BUDGET_PERIOD VALUES (2005); -- annual expenditure data CREATE TABLE EXPENDITURE (BP smallint NOT NULL, AMOUNT DECIMAL(15,2)); INSERT INTO EXPENDITURE VALUES (1999, 0.00); INSERT INTO EXPENDITURE VALUES (2000, 1.00); INSERT INTO EXPENDITURE VALUES (2001, 2.00); INSERT INTO EXPENDITURE VALUES (2002, 3.00); INSERT INTO EXPENDITURE VALUES (2003, 4.00); INSERT INTO EXPENDITURE VALUES (2004, NULL); -- calculate past years expenditure as of year: expected to be NULL for 1998, returns 0 SELECT A.BP, SUM( B.AMOUNT ) AS TOTAL_EXPD_ASOF FROM BUDGET_PERIOD A LEFT JOIN EXPENDITURE B ON (A.BP >= B.BP) GROUP BY A.BP ORDER BY A.BP -- same as above using CASE: returns all nulls (?!) SELECT A.BP, SUM( CASE WHEN A.BP >= B.BP THEN B.AMOUNT ELSE NULL END ) FROM BUDGET_PERIOD A, EXPENDITURE B GROUP BY A.BP go Regards, Vladimir
On Sat, Feb 28, 2009 at 04:01:51PM +0100, kelas wrote:
Dear MonetDB-users,
a complete newbie to MonetDB, I can't really tell whether it is a bug, feature or I'm just getting it all wrong.
A script below illustrates some weird NULL handling behaviour found in Nov2008-SP2:
You right it should be NULL instead of '0' for 1998. With the current stable (Feb2008 release) at least the second bug is gone. Unfortunately not yet the 'NULL' vs '0'. Niels
-- years under audit CREATE TABLE BUDGET_PERIOD (BP smallint NOT NULL); INSERT INTO BUDGET_PERIOD VALUES (1998); INSERT INTO BUDGET_PERIOD VALUES (1999); INSERT INTO BUDGET_PERIOD VALUES (2000); INSERT INTO BUDGET_PERIOD VALUES (2001); INSERT INTO BUDGET_PERIOD VALUES (2002); INSERT INTO BUDGET_PERIOD VALUES (2003); INSERT INTO BUDGET_PERIOD VALUES (2004); INSERT INTO BUDGET_PERIOD VALUES (2005);
-- annual expenditure data CREATE TABLE EXPENDITURE (BP smallint NOT NULL, AMOUNT DECIMAL(15,2)); INSERT INTO EXPENDITURE VALUES (1999, 0.00); INSERT INTO EXPENDITURE VALUES (2000, 1.00); INSERT INTO EXPENDITURE VALUES (2001, 2.00); INSERT INTO EXPENDITURE VALUES (2002, 3.00); INSERT INTO EXPENDITURE VALUES (2003, 4.00); INSERT INTO EXPENDITURE VALUES (2004, NULL);
-- calculate past years expenditure as of year: expected to be NULL for 1998, returns 0 SELECT A.BP, SUM( B.AMOUNT ) AS TOTAL_EXPD_ASOF FROM BUDGET_PERIOD A LEFT JOIN EXPENDITURE B ON (A.BP >= B.BP) GROUP BY A.BP ORDER BY A.BP
-- same as above using CASE: returns all nulls (?!) SELECT A.BP, SUM( CASE WHEN A.BP >= B.BP THEN B.AMOUNT ELSE NULL END ) FROM BUDGET_PERIOD A, EXPENDITURE B GROUP BY A.BP go
Regards, Vladimir
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