1 | #pragma once |
2 | |
3 | #include <memory> |
4 | #include <DataTypes/IDataType.h> |
5 | #include <AggregateFunctions/IAggregateFunction.h> |
6 | |
7 | |
8 | namespace DB |
9 | { |
10 | |
11 | /** Aggregate function combinator allows to take one aggregate function |
12 | * and transform it to another aggregate function. |
13 | * |
14 | * In SQL language they are used as suffixes for existing aggregate functions. |
15 | * |
16 | * Example: -If combinator takes an aggregate function and transforms it |
17 | * to aggregate function with additional argument at end (condition), |
18 | * that will pass values to original aggregate function when the condition is true. |
19 | * |
20 | * More examples: |
21 | * |
22 | * sum(x) - calculate sum of x |
23 | * sumIf(x, cond) - calculate sum of x for rows where condition is true. |
24 | * sumArray(arr) - calculate sum of all elements of arrays. |
25 | * |
26 | * PS. Please don't mess it with so called "combiner" - totally unrelated notion from Hadoop world. |
27 | * "combining" - merging the states of aggregate functions - is supported naturally in ClickHouse. |
28 | */ |
29 | |
30 | class IAggregateFunctionCombinator |
31 | { |
32 | public: |
33 | virtual String getName() const = 0; |
34 | |
35 | virtual bool isForInternalUsageOnly() const { return false; } |
36 | |
37 | /** From the arguments for combined function (ex: UInt64, UInt8 for sumIf), |
38 | * get the arguments for nested function (ex: UInt64 for sum). |
39 | * If arguments are not suitable for combined function, throw an exception. |
40 | */ |
41 | virtual DataTypes transformArguments(const DataTypes & arguments) const |
42 | { |
43 | return arguments; |
44 | } |
45 | |
46 | /** From the parameters for combined function, |
47 | * get the parameters for nested function. |
48 | * If arguments are not suitable for combined function, throw an exception. |
49 | */ |
50 | virtual Array transformParameters(const Array & parameters) const |
51 | { |
52 | return parameters; |
53 | } |
54 | |
55 | /** Create combined aggregate function (ex: sumIf) |
56 | * from nested function (ex: sum) |
57 | * and arguments for combined agggregate function (ex: UInt64, UInt8 for sumIf). |
58 | * It's assumed that function transformArguments was called before this function and 'arguments' are validated. |
59 | */ |
60 | virtual AggregateFunctionPtr transformAggregateFunction( |
61 | const AggregateFunctionPtr & nested_function, |
62 | const DataTypes & arguments, |
63 | const Array & params) const = 0; |
64 | |
65 | virtual ~IAggregateFunctionCombinator() {} |
66 | }; |
67 | |
68 | using AggregateFunctionCombinatorPtr = std::shared_ptr<const IAggregateFunctionCombinator>; |
69 | |
70 | } |
71 | |