cross apply behaves like outer apply

Question

cross apply behaves like outer apply

atsql

Right there with Babe

Points: 740
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August 26, 2014 at 5:31 pm

#145216

In my example, cross apply generates 5 rows when sum is used and 3 rows when no aggregate statement is used. Why cross apply generates 5 rows when SUM() used? I would expect such behavior when outer apply used.
IF OBJECT_ID('TempDB..#payment','U') IS NOT NULL
DROP TABLE #payment
IF OBJECT_ID('TempDB..#certificate','U') IS NOT NULL
DROP TABLE #certificate
CREATE TABLE #payment
(
paynum INT PRIMARY KEY,
payamount decimal
)
CREATE TABLE #certificate
(
gcnumber INT IDENTITY(1,1) PRIMARY KEY CLUSTERED,
paynum INT,
gcamount decimal
)
insert #payment (paynum, payamount) values(1, 30)
insert #payment (paynum, payamount) values(2, 35)
insert #payment (paynum, payamount) values(3, 37)
insert #payment (paynum, payamount) values(4, 49)
insert #payment (paynum, payamount) values(5, 68)
insert #certificate (paynum, gcamount) values(1, 5)
insert #certificate (paynum, gcamount) values(2, 7)
insert #certificate (paynum, gcamount) values(2, 3)
select p.paynum, c.gcamount from #payment p
cross APPLY(
SELECT SUM(gcamount) gcamount
FROM #certificate c
WHERE c.paynum = p.paynum
)c
select p.paynum, c.gcamount from #payment p
cross APPLY(
SELECT gcamount
FROM #certificate c
WHERE c.paynum = p.paynum
)c

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Luis Cazares SSC Guru Points: 183698 More actions · Answer 1

It's a little confuse, but the problem is that you're returning the value of a function and not a row or group of rows. Would that make sense to you?

Luis C.
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brad.mason5 Hall of Fame Points: 3299 More actions · Answer 2

Yes actually that is behavior I have seen as well when an aggregate is used in the query.

In order to eliminate the NULL values you will need to group the data. If a GROUP BY is not used or check for NULL is not in where condition and will get unexpected results.

select p.paynum, c.gcamount from #payment p

cross APPLY(

SELECT SUM(gcamount) gcamount

FROM #certificate c

WHERE c.paynum = p.paynum

GROUP BY c.paynum

)c

atsql Right there with Babe Points: 740 More actions · Answer 3

Thank you Brad for your response,

CROSS APPLY should behave like INNER JOIN. And yet with aggregates it behaves like OUTER APPLY or LEFT JOIN. I am wondering if there is Microsoft explanation for such behavior.