migrate-to-nql

name: migrate-to-nql description: Migrate React components from Snowflake SQL queries to NQL using the useNqlQuery hook. Handles query design, case sensitivity, and React dependency optimization. argument-hint: "[file-or-component]"

Migrate the queries used in: $ARGUMENTS from using Snowflake SQL to NQL.

Migrating from SQL Queries to NQL Queries

This guide provides instructions for migrating React components from SQL-based data fetching to NQL-based queries using the useNqlQuery hook.

Overview

NQL (Narrative Query Language) queries create temporary materialized views and then sample the data, requiring a different approach than direct SQL execution. The process involves:

1. Query submission -> Job polling -> Materialized view creation
2. Sample request -> Job polling -> Sample preparation
3. Data fetching -> Final results

Step-by-Step Migration Process

1. Identify the Current Implementation

Look for:

• Direct SQL query execution (e.g., useDatasetRows, useSqlQuery)
• Components fetching tabular data with filters/transformations
• Data processing logic that could be moved to the database level

Example Pattern:

// OLD: Direct data fetching + client-side processing
const { data: rawData } = useDatasetRows(datasetName);
const processedData = rawData?.map(row => /* complex processing */) || [];

2. Design the NQL Query

Do:

• Write pure SQL SELECT statements for the core query logic
• Use SQL aggregations, filters, and transformations instead of client-side processing
• Include appropriate WHERE clauses and LIMIT statements
• Use proper column aliases (e.g., as label_value)

Don't:

• Include CREATE MATERIALIZED VIEW statements (handled by useNqlQuery)
• Use database-specific syntax that's not supported in NQL
• Forget to handle NULL values and empty strings in WHERE clauses
• Don't use '*' anywhere
• Prefix tables with company_data

Example:

SELECT DISTINCT
    CONCAT_WS(' > ', CATEGORY, SUB_CATEGORY) as label_value
FROM company_data.{datasetName}
WHERE CONCAT_WS(' > ', CATEGORY, SUB_CATEGORY) IS NOT NULL
    AND CONCAT_WS(' > ', CATEGORY, SUB_CATEGORY) <> ''
LIMIT 1000

3. Create the NQL Hook

Structure:

export function useCustomNqlQuery(
    // Stable primitive parameters
    param1: string | undefined,
    param2: number | null,
    // Complex objects (handle carefully)
    complexData: ComplexType[],
): QueryResult {
    // Extract stable dependencies first
    const stableDependency = useMemo(() => {
        return complexData.find(item => item.id === param1)?.relevantField;
    }, [param1, complexData]);

    // Build query with stable dependencies
    const nqlQuery = useMemo(() => {
        if (!param1 || !stableDependency) return "";

        return `
            SELECT column1, column2
            FROM dataset.${param1}
            WHERE condition = '${stableDependency}'
            LIMIT 1000
        `.trim();
    }, [param1, stableDependency]);

    const { data: rawData, error, isLoading } = useNqlQuery(nqlQuery, {
        enabled: !!nqlQuery,
    });

    // Memoize data transformation
    const transformedData = useMemo(() => {
        if (!rawData) return null;

        return rawData.map((row, index) => ({
            id: `${row.COLUMN1}_${index}`, // Stable, unique IDs
            value: String(row.COLUMN1 || row.column1 || ""),
            // ... other transformations
        }));
    }, [rawData]);

    return { data: transformedData, error, isLoading };
}

4. Handle Case Sensitivity

Issue: NQL results may return uppercase column names even if your query uses lowercase aliases.

Solution:

// Handle both cases in data access
const value = String(row.LABEL_VALUE || row.label_value || "");

Type Definition:

type NqlResult = {
    LABEL_VALUE?: string;  // Uppercase (what may be returned)
    label_value?: string;  // Lowercase (what you expect)
};

5. Optimize React Dependencies

Critical Issues to Avoid:

Infinite Re-renders

Problem: Large objects in dependencies cause constant re-computation

// BAD: Entire array causes re-renders
const query = useMemo(() => buildQuery(), [largeArray]);

Solution: Extract only what you need

// GOOD: Stable dependencies
const specificItem = useMemo(() =>
    largeArray.find(item => item.id === targetId),
    [targetId, largeArray]
);
const query = useMemo(() => buildQuery(specificItem), [specificItem]);

Unstable Transforms

Problem: Data transformation creates new objects on every render

// BAD: Creates new objects every render
const data = rawData?.map(row => ({ ...row, processed: true }));

Solution: Memoize transformations

// GOOD: Stable object references
const data = useMemo(() =>
    rawData?.map(row => ({ ...row, processed: true })),
    [rawData]
);

6. Update Component Usage

Replace old hook calls:

// OLD
const { data, isLoading, error } = useDatasetRows(datasetId);

// NEW
const { data, isLoading, error } = useCustomNqlQuery(
    selectedAttribute,
    datasetName,
    referenceDatasets
);

Update error handling:

// Handle NQL-specific errors
useEffect(() => {
    if (error) {
        dispatch({
            type: "ui/setError",
            payload: `Failed to load data: ${error.message}`,
        });
    }
}, [error, dispatch]);

7. Test and Debug

Add Temporary Debugging:

console.log('[CustomNqlQuery] Query:', nqlQuery);
console.log('[CustomNqlQuery] Raw data:', rawData);
console.log('[CustomNqlQuery] Transformed:', transformedData);

Monitor for:

• Infinite re-renders (check browser console for repeated logs)
• Cache invalidation issues (datasets not appearing)
• Case sensitivity problems (undefined values in transforms)
• Performance issues (unnecessary re-computations)

Remove debugging once stable

Common Pitfalls and Solutions

1. Infinite Loops

Cause: Unstable dependencies in useMemo/useCallback Solution: Use primitive values or properly memoized objects as dependencies

2. Cache Issues

Cause: New datasets not appearing in dropdowns Solution: Cache invalidation Usually resolves automatically; avoid manual cache invalidation

3. Data Structure Mismatches

Cause: Expecting lowercase but getting uppercase column names Solution: Handle both cases in data access and type definitions

4. Component Re-render Cascades

Cause: Parent components passing unstable props Solution: Memoize expensive computations and use stable object references

Best Practices

1. Start with the simplest possible NQL query and add complexity gradually
2. Use browser dev tools to monitor component re-renders and network requests
3. Write TypeScript interfaces that handle both uppercase and lowercase field names
4. Memoize all data transformations to prevent infinite loops
5. Test with different datasets to ensure robustness
6. Keep query logic in the database rather than client-side processing
7. Use descriptive console logging during development, remove in production

Example Migration

Before (SQL-based):

const { data: datasetRows } = useDatasetRows(datasetName);
const uniqueLabels = useMemo(() => {
    // Complex client-side processing
    const values = new Map();
    datasetRows?.forEach(row => {
        const value = row[columnName];
        if (value) values.set(value, (values.get(value) || 0) + 1);
    });
    return Array.from(values.entries()).map(([value, count], index) => ({
        id: `label_${index}`,
        value,
        count
    }));
}, [datasetRows, columnName]);

After (NQL-based):

const { data: uniqueLabels } = useNqlLabelsQuery(
    selectedAttribute,
    datasetName,
    referenceDatasets
);

// Much simpler - processing moved to database level
// Returns stable, memoized results

Performance Benefits

• Reduced client-side processing: Complex logic handled at database level
• Better caching: Materialized views can be reused
• Improved scalability: Works with larger datasets without client memory issues
• Consistent results: Database-level processing ensures consistent output

When NOT to Use NQL

• Simple, static queries that don't benefit from materialized views
• Real-time data requirements (due to polling overhead)
• Very small datasets where client-side processing is more efficient
• Cases where you need streaming or incremental updates