feat: add function rewrite rule for json_get with cast

[sunng87]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

What's changed and what's your intention?

This patch provides support for sql like

SELECT json_get(parse_json('{"a":1}'), 'a')::text;

SELECT json_get(parse_json('{"a":1}'), 'a')::int8;

It also changes the third argument of json_get to accept value type instead of type name.

Note that we have a sql transform rewrite type_alias that rewrites ::int8 to arrow_cast function calls. So we will deal with both arrow_cast function call and cast expression here.

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[gemini-code-assist]

Summary of Changes

Hello @sunng87, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the SQL query engine's capabilities by introducing a robust function rewrite framework. This framework is immediately leveraged to provide more intuitive and powerful type casting for the json_get function, allowing users to directly specify the desired return type using standard SQL cast syntax. This change streamlines JSON data extraction and type conversion, making queries more concise and user-friendly.

Highlights

• Function Rewrite Mechanism: Introduced a new FunctionRewrite mechanism within the FunctionRegistry to allow for dynamic modification of expressions in the query plan. This enables more flexible and powerful SQL syntax transformations.
• JSON_GET Type Casting Support: Implemented a JsonGetRewriter that specifically handles json_get function calls followed by a type cast (e.g., json_get(..., 'path')::int). This rewriter transforms the expression json_get(expr, path)::type into json_get(expr, path, NULL::type).
• Enhanced JSON_GET Function: The json_get function's JsonGetWithType variant was updated to interpret this new third argument (NULL::type) to infer the desired return type, simplifying type conversion for JSON extraction.
• Query Optimizer Integration: The ApplyFunctionRewrites analyzer rule was integrated into the query planning and optimization pipeline, ensuring that registered function rewrite rules, like the JsonGetRewriter, are applied during logical plan analysis.

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[gemini-code-assist]

Code Review

This pull request introduces a function rewrite rule to support CAST operations on the json_get function, allowing for a more natural SQL syntax like json_get(...)::type. The implementation involves creating a FunctionRewrite rule, registering it with the query engine, and modifying the json_get function to handle the rewritten expression.

My review has found a critical issue where the new functionality appears to be broken in the provided tests. Additionally, I've identified a potential robustness issue in the new rewrite rule. Please see my detailed comments.

[waynexia]

@codex review

[chatgpt-codex-connector]

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Reviewed commit: 9ef77cd07f

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[sunng87]

Convert to draft for now. I'm going to remove the arrow_cast trasformation in type_alias.rs if possible. That will simplify the rewrite quite a bit.

Update: not removable. We still need arrow_cast for timestamps

[killme2008]

@sunng87 I think this feature could be implemented as a TransformRule:

greptimedb/src/sql/src/statements/transform.rs

Line 38 in 279b009

pub(crate) trait TransformRule: Send + Sync {

Similar to how type aliasing is handled:

https://github.com/GreptimeTeam/greptimedb/tree/main/src/sql/src/statements/transform

It doesn't need to be implemented as an analyzer rule.

[sunng87]

@killme2008 Yes it's possible. This change is to use datafusion function rewriter API: https://docs.rs/datafusion/latest/datafusion/logical_expr/expr_rewriter/trait.FunctionRewrite.html and make this API work on our implementation.

[killme2008]

@sunng87 Conflicts must be resolved.