[CALCITE-237] Allow user-defined aggregate functions (UDAs) to be defined in a model

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Labels: github-import
• Assignee: Unassigned
• Reporter: GitHub Import
• Created: 18/Jun/14 08:45
• Updated: 18/Jun/14 08:46
• Resolved: 18/Jun/14 08:46

Description

Allow user-defined aggregate functions (UDAs) to be defined in a model, using a simple class to implement the UDA.

A class can implement a UDA if it has init and add methods, and optionally initAdd, merge and result. For example,

```java
class MySumAggFun {
public MySumAggFun() {}
public long[] init();
public long[] initAdd(int v);
public void add(long[] accumulator, int v);
public long[] merge(long[] accumulator0, long[] accumulator1);
public long result(long[] accumulator);
}
```

Every UDA has argument types (in general it can be a list with 0 or more elements, but usually 1), accumulator type, and result type. These are inferred from the method signatures.

In this example, the accumulator type is `long[]`, the argument type is `[int]`, and the result type is `long`.

If there is no `result` method, the accumulator and result types are the same, and the result is just the accumulator.

If there is no `initAdd` method, Optiq calls `init` followed by `add`.

The methods can all be static, in which case the class does not need a public zero-argument constructor.

Example model:

```json
schemas: {
{
name: ‘HR’,
functions: [

{ name: ‘MY_SUM’, className: ‘com.example.MySumAggFun’ }

]
}
```

---------------- Imported from GitHub ----------------
Url: https://github.com/julianhyde/optiq/issues/237
Created by: julianhyde
Labels:
Created at: Sun Apr 06 23:31:50 CEST 2014
State: closed