confluentinc/ksql

Support FIND_FIRST Lambda Function

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#7,387 建立於 2021年4月15日

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 (2 留言) (0 反應) (0 負責人)Java (5,739 star) (1,048 fork)batch import
enhancementgood first issuestreaming-engine

描述

Is your feature request related to a problem? Please describe.

A user requested the ability to map an array into fields where the arrays have some predefined set of values:

Sample Data: 
 - FOO: [{"key":"a", "val":2}, {"key":"b", "val":4}]
 - FOO: [{"key":"b", "val":3}]
 
Sample Output:

| a | b |
|---|---|
| 2 | 4 |
|nul| 3 |

Describe the solution you'd like

We could implement FIND_FIRST(array, x -> predicate(x)) lambda function and implement this as:

SELECT FIND_FIRST(FOO, x -> x = 'a') AS a, FIND_FIRST(FOO, x -> x = 'b') AS b FROM source;

Describe alternatives you've considered

Implement PIVOT - this is a little bit more involved and this is a good general use case for lambdas.

貢獻者指南

技術棧
javasql
領域
database
議題類型
feature
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
4
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
3-5 days
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
Familiarity with KSQLKnowledge of SQL lambda functionsJava programming experience
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
30
研究方向
To implement FIND FIRST, start by examining how existing lambda functions like FILTER are defined in the KSQL codebase. Look at the parser (e.g., SqlLambda.java) and the runtime evaluation logic. Identify the relevant stages: parsing the lambda expression, type checking, and executing the function. The changes will likely involve adding a new function definition in the function registry, handling the new SQL syntax in the parser, and implementing the evaluation logic.