SQL Parser
The SQL parser (server/src/sqp_parser.rs) implements a restricted SQL dialect called “Simplified SQL” that prevents expensive or dangerous operations. It uses the sqlparser crate with the ANSI dialect.
Supported SQL Features
SELECT Clause
- Wildcard:
SELECT * - Named columns:
SELECT col1, col2 - Aliases:
SELECT col1 AS alias - No expressions, functions, or computed columns
FROM Clause
- Single table only:
FROM my_table - No table aliases
- No JOINs
WHERE Clause
- Comparison operators:
=,!=,<,>,<=,>= - Boolean:
IS TRUE,IS FALSE,IS NULL,IS NOT NULL - Range:
BETWEEN ... AND ...,NOT BETWEEN - Set membership:
IN (...),NOT IN (...) - Pattern matching:
LIKE,ILIKE,SIMILAR TO - Logical operators:
AND,OR,NOT - Nested expressions with parentheses
- Type casting:
CAST(... AS ...),TRY_CAST,:: - String functions:
SUBSTRING,TRIM,OVERLAY,POSITION - Math functions:
CEIL,FLOOR - Time functions:
EXTRACT,AT TIME ZONE - Literals: strings, numbers, booleans, NULL, arrays, intervals
ORDER BY
- Column references
ASC/DESCNULLS FIRST/NULLS LAST
LIMIT / OFFSET
LIMIT nOFFSET n
Explicitly Unsupported
The parser rejects queries containing:
| Feature | Reason |
|---|---|
| JOINs | Prevents cross-table operations |
| GROUP BY / HAVING | No aggregation |
| Subqueries | No nested queries |
CTEs (WITH) | No common table expressions |
| UNION / INTERSECT / EXCEPT | No set operations |
| Window functions | No analytical functions |
Aggregate functions (COUNT, SUM, etc.) | No aggregation in SELECT |
| DISTINCT | No deduplication |
Qualified wildcards (alias.*) | No table-qualified wildcards |
LIMIT BY | MySQL-specific syntax |
ORDER BY ALL | Not supported |
Analyzed Query Structure
The parser produces an AnalyzedQuery struct:
#![allow(unused)]
fn main() {
pub struct AnalyzedQuery {
pub body: AnalyzedSelect, // SELECT/FROM/WHERE
pub limit_clause: Option<AnalyzedLimitClause>,
pub order_by: Option<Vec<AnalyzedOrderByExpr>>,
}
pub struct AnalyzedSelect {
pub projection: Vec<AnalyzedSelectItem>, // Column list
pub wildcard: bool, // Was * used?
pub from: String, // Table name
pub selection: Option<Expr>, // WHERE clause AST
}
}The WHERE clause retains the sqlparser Expr AST nodes, which are validated to contain only supported expression types.
Row Count Estimation
The parser provides create_estimate_rows_query which wraps any valid query in a SELECT COUNT(*):
#![allow(unused)]
fn main() {
pub fn create_estimate_rows_query(duckdb_sql: &str) -> String {
format!("SELECT COUNT(*) as num_rows FROM ({})", duckdb_sql)
}
}This is used in Phase 1 to estimate pricing without executing the full query.