Package edu.caltech.nanodb.functions

This package contains the abstractions for supporting simple functions, aggregate functions, and table-returning functions in NanoDB. Additionally, this package contains many function implementations to use in SQL queries, as well as a FunctionDirectory for looking up function implementations from within the query planning and evaluation code.

Here is a brief description of the abstractions implemented in NanoDB.

• All kinds of functions derive from the abstract Function base class.
• "Simple functions" take zero or more arguments, and produce one result for each set of inputs. They may be deterministic or nondeterministic, and they may access or maintain state data. All simple functions derive from the SimpleFunction class.
• "Aggregate functions" take a multiset of inputs, and produce one aggregate result from that multiset of inputs. Currently, aggregate functions only accept one multiset (e.g. AVG(n)). All aggregate functions derive from the AggregateFunction class.
• Both simple functions and aggregate functions derive from the ScalarFunction class, since both of them return a single result value, and both can appear in expressions.
• "Table functions" take zero or more arguments, and return a result-set of zero or more tuples. Table functions have an interface similar to the plan-node interface so that tuples can be produced one at a time, and other details such as schema and costing details can be exposed by the function.

Function Naming

All function names are uppercase.

Aggregate functions may support the DISTINCT keyword, e.g. "SELECT COUNT(DISTINCT a) FROM t;". In NanoDB, these invocations are mapped to a function invocation with "#DISTINCT" appended to the specified function name. For example, the example SQL will result in NanoDB resolving the invocation to the "COUNT#DISTINCT" function.

Class Summary

Class	Description
Abs	Implementation of the ABS(x) SQL function, computes the absolute value of a single argument.
AggregateFunction	This class provides the general abstraction for aggregate functions.
ArcCos	Implementation of the ACOS(x) SQL function, computes the arc-cosine of a single argument.
ArcSin	Implementation of the ASIN(x) SQL function, computes the arc-sine of a single argument.
ArcTan	Implementation of the ATAN(x) SQL function, computes the arc-tangent of a single argument.
ArcTan2	Implementation of the ATAN2(y, x) SQL function, computes the arc-tangent of two arguments.
Avg	Implementation of the AVG(x) SQL aggregate function, computes the average of its inputs.
AvgDistinct	Implementation of the AVG(DISTINCT x) SQL aggregate function, computes the average of its inputs.
Ceil	Implementation of the CEIL(x) / CEILING(x) SQL function, computes the smallest whole number larger than the argument.
Coalesce	Implementation of the COALESCE(a, b, ...) SQL function, returns the first non-NULL argument.
Concat	Implementation of the CONCAT(s1, s2, ...) SQL function, concatenates two or more arguments as strings.
Cos	Implementation of the COS(x) SQL function, computes the cosine of a single argument.
Count	Created by donnie on 12/6/13.
CountAggregate	This aggregate function can be used to compute both COUNT(...) and COUNT(DISTINCT ...) aggregate functions.
CountDistinct	Created by donnie on 12/7/13.
CountStar	Created by donnie on 11/1/14.
Floor	Computes the largest whole number smaller than the argument.
Function	This is the root class of all kinds of functions in NanoDB.
FunctionDirectory	This class is a directory of all functions recognized within NanoDB, including simple functions, aggregate functions and table functions.
Greatest	Returns the greatest value of all arguments.
If	Implements IF (cond, expr1, expr2).
IfNull	Implements IFNULL(expr1, expr2).
Least	Returns the least value of all arguments.
Max	Created by donnie on 12/7/13.
Min	Created by donnie on 12/7/13.
MinMaxAggregate	This aggregate function can be used to compute either the minimum or the maximum of a collection of values.
NullIf	Implements NULLIF(cond, expr).
Pow	Returns the first argument, raised to the second argument power.
ReadPerfCounter	Returns the current value of the specified performance counter.
ResetPerfCounter	Resets the specified performance counter, and returns the old value.
Round	Computes the whole number that is closest to the argument.
ScalarFunction	This class represents functions that return a scalar value.
SimpleFunction	Created by donnie on 12/5/13.
Sin	Implementation of the SIN(x) SQL function, computes the sine of a single argument.
Sqrt	Computes the square root of a single argument.
StdDev	Created by donnie on 12/7/13.
StdDevVarAggregate	This aggregate function can be used to compute either the standard deviation or the variance of a collection of values.
Sum	Created by donnie on 12/7/13.
SumAvgAggregate	This aggregate function can be used to compute both SUM and AVERAGE functions.
SumDistinct	Created by donnie on 12/7/13.
TableFunction	This is the base-class for all table-returning functions.
Tan	Implementation of the TAN(x) SQL function, computes the tangent of a single argument.
Variance	Created by donnie on 12/7/13.