feat: topk in group by in counts api

[nikhilsinhaparseable]

current: counts api returns the date binned result for each distinct value for the field(s) present in group by

if the field used is high cardinal, the response will be bloated
Prism uses this response to build a chart that might crash in render

change: add optional topk param to group by
default to 10
api returns topk results for the group by field(s)

Summary by CodeRabbit

• New Features

  • Added support for limiting count and group-by results with a top-N setting.
  • Enabled flexible input names for the new setting in requests.

• Bug Fixes

  • Improved SQL generation to correctly quote identifiers.
  • Adjusted grouped count queries to return only the highest-ranking groups.
  • Added validation to reject invalid zero-value top-N requests.

[coderabbitai]

Walkthrough

src/query/mod.rs adds a top_k parameter to CountConditions and reworks get_df_sql to emit WITH grouped_counts/top_groups CTEs when group-by columns are present, limiting results to the top N groups. A quote_identifier helper is added, a DEFAULT_COUNTS_TOP_K constant introduced, and zero-value validation enforced.

Changes

top_k support for grouped count queries

Layer / File(s)	Summary
Constant, CountConditions.top_k field, and quote_identifier helper src/query/mod.rs	Adds DEFAULT_COUNTS_TOP_K constant, extends CountConditions with top_k: Option<usize> accepting topk/top_k serde aliases, and adds private quote_identifier function for safe SQL identifier embedding.
get_df_sql identifier quoting and top-K grouped query generation src/query/mod.rs	Quotes table name, time column, and group-by column identifiers in get_df_sql. For ungrouped queries emits a plain SELECT; for grouped queries builds WITH grouped_counts and top_groups CTEs, defaulting top_k to DEFAULT_COUNTS_TOP_K and rejecting top_k == 0.
Tests for deserialization, SQL shape, defaulting, and zero rejection src/query/mod.rs	Adds tests covering topK/topk JSON deserialization into CountConditions.top_k, the generated SQL CTE structure for grouped queries, default top_k fallback behavior, and the error returned for top_k = 0.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• parseablehq/parseable#1601: Modifies the same get_df_sql function in src/query/mod.rs to add group_clause to the grouped counts SELECT/GROUP BY/ORDER BY, directly preceding the top-K restructuring introduced here.

Poem

🐇 Hippity-hop through SQL rows,
With top_k now, the count query flows!
A CTE here, a subquery there,
No zero allowed — we handle with care.
The top groups rise, the rest stand down,
This bunny built a query crown! 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the main change: adding topk support to counts group-by responses.
Description check	✅ Passed	The description explains the problem, the proposed change, and the default behavior, though it omits the template's issue link and checklist details.
Docstring Coverage	✅ Passed	Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/query/mod.rs (1)

1063-1078: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Cover the top_k alias in the deserialization test.

The struct explicitly accepts top_k, but this test only locks topK and topk. Add one assertion for the snake_case request key.

Suggested test addition

         let conditions: CountConditions = serde_json::from_value(json!({
             "groupBy": ["host"],
             "topk": 3
         }))
         .unwrap();
         assert_eq!(conditions.top_k, Some(3));
+
+        let conditions: CountConditions = serde_json::from_value(json!({
+            "groupBy": ["host"],
+            "top_k": 7
+        }))
+        .unwrap();
+        assert_eq!(conditions.top_k, Some(7));

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/query/mod.rs` around lines 1063 - 1078, The CountConditions
deserialization test only verifies the camelCase and lowercase aliases, so add
one assertion for the snake_case request key to cover the explicitly supported
top_k field. Update test_count_conditions_accepts_top_k in src/query/mod.rs to
deserialize a payload using top_k and assert it maps to conditions.top_k,
alongside the existing topK and topk checks.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/query/mod.rs`:
- Around line 721-722: The top_groups subquery in the query-building logic uses
ORDER BY SUM("count") DESC LIMIT {top_k}, which can return different tied groups
across runs. Update the ordering in the top_groups SELECT to append the group
columns as a deterministic tie-breaker after the count sort, keeping the change
within the formatted SQL assembled in src/query/mod.rs near the
grouped_counts/top_groups query construction.

---

Nitpick comments:
In `@src/query/mod.rs`:
- Around line 1063-1078: The CountConditions deserialization test only verifies
the camelCase and lowercase aliases, so add one assertion for the snake_case
request key to cover the explicitly supported top_k field. Update
test_count_conditions_accepts_top_k in src/query/mod.rs to deserialize a payload
using top_k and assert it maps to conditions.top_k, alongside the existing topK
and topk checks.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

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Run ID: 705e634b-9fb7-4f48-8516-3ab0cd55a458

📥 Commits

Reviewing files that changed from the base of the PR and between 1998658 and aacfe91.

📒 Files selected for processing (1)

• src/query/mod.rs