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❑ CHECKSUM_AGG
❑ COUNT
❑ COUNT_BIG
❑ GROUPING
❑ MAX
❑ MIN
❑ STDEV
❑ STDEVP
❑ SUM
❑ VAR
❑ VARP
In most aggregate functions, the ALL or DISTINCT keywords can be used. The ALL argument is the
default and will apply the function to all the values in the expression, even if a value appears numerous
times. The DISTINCT argument means that a value will only be included in the function once, even
if it occurs several times.
Aggregate functions cannot be nested. The expression cannot be a subquery.
AVG
AVG returns the average of the values in expression. The syntax is as follows:
AVG([ALL | DISTINCT] )
The expression must contain numeric values. NULL values are ignored. This function supports the
OVER operator described in the ranking functions section of this appendix.
CHECKSUM
This is a basic hash algorithm usually used to detect changes or consistency in data. This particular function
accepts either an expression as an argument or a * (which implies that you want all columns in all
the joined tables to be included). The basic syntax is:
CHECKSUM(, […n] | * )
Note that the order of your expression — or in the case of a *, the join order — will affect the checksum
value, so, for example:
CHECKSUM(SalesOrderID, OrderDate)
would not give the same result as:
CHECKSUM(OrderDate, SalesOrderID )
This function is NOT compatible with the OVER operator.
Apendix A: System Functions
591