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name: sql-research description: Guide for researching SQL syntax and behavior for database backends. Use when you need to research how a SQL function, command, or feature works in a specific database before implementing it in dbplyr.

SQL Research Skill

Use this skill when researching SQL syntax and behavior for any database backend before implementing translations or features in dbplyr.

When to use this skill

• Before implementing any SQL translation for a database backend
• When you need to understand SQL syntax, behavior, or edge cases
• When documenting database-specific SQL features
• Before writing SQL-generating code in dbplyr

Critical principle

SQL correctness is paramount in dbplyr. You MUST complete research and documentation BEFORE implementing any SQL-related code.

Research workflow

1. Search for official documentation

Use WebSearch to find official documentation for "{dialect} {function/command}":

• Prioritize official database documentation and reputable sources
• Search for syntax, behavior, edge cases, and version-specific differences
• Look for:
  • Function signatures and argument types
  • Return types and behavior
  • NULL handling
  • Type coercion rules
  • Limitations or restrictions
  • Differences across database versions

2. Document your findings

Create research/{dialect}-{command}.md with the following structure:

# {Dialect} - {Function/Command}

## Summary
[1-2 sentence summary focused on R-to-SQL translation]

## Syntax
[Minimal syntax examples from official sources]

## Key behaviors
[Only behaviors that matter for dbplyr translation]

## Limitations
[Only restrictions that affect dbplyr usage]

## Sources
- [Source name](URL)
- [Source name](URL)

Documentation guidelines:

• Keep it minimal and focused on dbplyr use cases
• Include only what's relevant to translating R code to SQL
• ALL citations with URLs are REQUIRED (no exceptions)
• NO comparisons with other databases
• Use concrete examples from official sources
• Keep it as concise as possible

3. Verify your research

Cross-reference multiple sources when:

• Documentation seems incomplete or unclear
• Behavior differs across database versions
• Edge cases aren't well documented
• Official docs contradict community sources

Best practices:

• Check at least 2-3 authoritative sources
• Note any version-specific differences
• Document uncertainties or ambiguities
• When in doubt, test with actual database if possible

4. Proceed to implementation

Only after completing research and documentation should you:

• Implement SQL translations
• Write SQL-generating code
• Add tests for the functionality

Example research files

Minimal example

# PostgreSQL - POSITION

## Summary
Returns the starting position of a substring within a string (1-indexed).

## Syntax
POSITION(substring IN string)

## Key behaviors
- Returns integer position (1-indexed)
- Returns 0 if substring not found
- Case-sensitive by default
- NULL if any argument is NULL

## Sources
- [PostgreSQL String Functions](https://www.postgresql.org/docs/current/functions-string.html)

Complex example

# SQL Server - STRING_AGG

## Summary
Concatenates string values with a specified separator, optionally ordering results.

## Syntax
STRING_AGG(expression, separator) [WITHIN GROUP (ORDER BY order_expression)]

## Key behaviors
- Available in SQL Server 2017+ (compatibility level 110+)
- Returns NULL for empty groups
- Separator must be a literal or variable, not an expression
- WITHIN GROUP clause is optional but commonly used for deterministic ordering
- Maximum output length is 2GB

## Limitations
- Not available in SQL Server 2016 or earlier
- Cannot use with DISTINCT (use subquery instead)
- Separator cannot be a computed expression

## Sources
- [SQL Server STRING_AGG](https://docs.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql)
- [Compatibility requirements](https://docs.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql#compatibility-support)

Common research patterns

String functions

• Character encoding and collation
• 0-indexed vs 1-indexed positions
• NULL handling
• Regular expression support and syntax

Date/time functions

• Date/time types and precision
• Timezone handling
• Format strings and conventions
• Interval arithmetic

Aggregate functions

• NULL handling in aggregates
• Empty group behavior
• DISTINCT support
• Window function variants

Window functions

• OVER clause syntax
• Frame specifications (ROWS vs RANGE)
• Partitioning and ordering
• Function-specific restrictions

Checklist

Before completing SQL research:

• Searched official database documentation
• Identified syntax and key behaviors
• Documented edge cases and limitations
• Created research file in research/{dialect}-{function}.md
• Included ALL source URLs
• Kept documentation minimal and focused
• Cross-referenced multiple sources if needed
• Ready to proceed with implementation

Tips

• Start broad, then narrow: Search for the general command first, then dig into specifics
• Use official docs first: Official documentation is most authoritative
• Check version availability: Many SQL features are version-specific
• Note NULL behavior: NULL handling often differs across databases
• Document what matters: Focus on dbplyr translation needs, not general SQL education
• Keep it short: Research docs should be scannable reference material, not tutorials