Use of aggregate functions

Aggregate functions in the statistics of a ~, are often common gray. But there's a little bit to be aware of.

Create Table#Tmp (AintBint )Insert  into#Tmp (A, B)Values(1,NULL),(NULL,NULL),(NULL,3),(2,4)Select *  from#Tmpa b----------- -----------1           NULLNULL        NULLNULL        32           4

Here I'll simply try using the count and Sum and AVG 3 most commonly used functions. This usage is very simple, just pay attention to the behavior of the null value in this area.

Select COUNT(*),COUNT(a),COUNT(A+b from#TmpSelect sum(a),sum(b),sum(A+b from#TmpSelect avg(a),avg(b*1.0),avg(A+b from#Tmp----------- ----------- -----------4           2           1                        ----------- ----------- -----------3           7           6                                                    ----------- --------------------------------------- -----------1           3.500000                                6

Note that when the row data contains a null value, the row data is filtered. COUNT (*) excepted

(*^__^*) hehe ...

Use of aggregate functions