wren-sql

Wren SQL

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Wren Engine translates SQL through a semantic layer (MDL — Model Definition Language) before executing it against a backend database. SQL must target MDL model names, not raw database tables.

For specific topics, load the relevant reference file:

Topic	Reference
SQL error diagnosis and correction	references/correction.md
Date/time functions and intervals	references/datetime.md
ARRAY, STRUCT, JSON/VARIANT types	references/types.md
BigQuery dialect quirks	references/bigquery.md

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Context

• You are querying a semantic layer, not a database directly.
• Only use model/view/column names defined in the MDL — never raw database table references.
• Wren Engine uses a generic SQL dialect similar to ANSI SQL (DataFusion/Postgres/DuckDB), but with differences.
• Check the dataSource field to identify the backend and apply dialect-specific rules if needed.

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Core SQL Rules

• Only SELECT statements. No DELETE, UPDATE, INSERT.
• Only use tables and columns from the MDL schema.
• Do not include comments in generated SQL.
• Prefer CTEs over subqueries.
• Identifiers are case-sensitive. Quote identifiers containing unicode, special characters (except _), or starting with a digit using double quotes.
  • Examples: "客户"."姓名", "table-name"."col", "123column"
• Identifier quotes: " (double quotes). String literal quotes: ' (single quotes).
• For specific date queries, use a range:

  WHERE ts >= CAST('2024-11-01 00:00:00' AS TIMESTAMP WITH TIME ZONE)
    AND ts <  CAST('2024-11-02 00:00:00' AS TIMESTAMP WITH TIME ZONE)
  

• For ranking, use DENSE_RANK() + WHERE. Include the ranking column in SELECT.
• Avoid correlated subqueries — use JOINs instead.
• Use SAFE_CAST when casting might fail: SAFE_CAST(col AS INT)