confluentinc/ksql

Support FIND_FIRST Lambda Function

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#7,387 创建于 2021年4月15日

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 (2 评论) (0 反应) (0 负责人)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.

贡献者指南

技术栈
javasql
领域
database
议题类型
feature
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
4
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
3-5 days
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Familiarity with KSQLKnowledge of SQL lambda functionsJava programming experience
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
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.