sqltk

sqltk is a toolkit for analysis and transformation of SQL statements, built on top of sqlparser.

Features

• A comprehensive Visitor trait and implementations for all sqlparser AST node types.

• A Transform trait for rewriting ASTs (sqltk does not provide a VisitorMut trait).

Comprehensive Visitor trait with more useful AST traversal order

sqlparser's Visitor implementation only contains callbacks for a handful of AST node types.

In contrast, sqltk's implementation will invoke Visitor::enter and Visitor::exit for all sqlparser node types.

Additionally, sqltk traverses the AST in an order that is useful for semantic analysis - specifically any node that might be referred to by another node will be visited before a node that might refer to it.

This means your Visitor implementations can safely assume that any semantic dependencies of the node being visited have already been visited.

For example, in a SELECT statement the FROM clause will be visited before the projection or the WHERE clause etc.

The analysis that determines AST traversal order happens at compile time (see packages/sqltk-codegen).

Transform trait

The Transform trait contains a single method imaginitively named transform. Which takes a reference to the original AST node and an owned clone of the node as arguments. Edits are applied to the owned node and returned in a Result.

The reason for this existence of this trait is so that metadata about nodes (from a previous analysis step) which inform the transformation process can be held in the type that implements Transform. These will be regular Rust shared references to AST nodes (and therefore read-only). Which would prevent mutation of the nodes in-place because Rust will not allow coexistence of &node and &mut node.

sqlparser's VisitorMut::visit_mut method accepts a &mut node argument, thus preventing coexistance of references to nodes in another data structure - which rules out the use of some patterns for associating metadata with those nodes.

Transformation begins at the leaf nodes of the AST (AKA depth-first) and ends at the root node.

Getting started

Add sqltk to your Cargo project

$ cargo add sqltk

If you plan to hack on sqltk itself then you will need to install cargo-expand if you plan on running the code generator.

$ cargo install cargo-expand

NOTE: cargo-expand invokes Rust nightly to do its job. Therefore a nightly Rust toolchain must be installed. However, sqltk's generated code does not require a nightly compiler.

sqltk-codegen

Analyses sqlparser source code and generates:

• Analyzes the sqlparser AST in order to determine an AST traversal order for single-pass semantic analysis workloads
• Generates the Visitable trait implementations for all AST node types
• Generates the Transformer trait implementations for all AST node types
• Generates the AsNodeKey trait implementations

To update:

# Run the code generation
cargo run -p sqltk-codegen

# Commit the changes
git a packages/sqltk/src/generated
git commit -m 'Re-generated trait implementations with `cargo run -p sqltk-codegen`'

You will need to do this whenever:

• You are updating sqltk-parser from upstream, and
• Any AST handling in sqltk-parser has changed

About

sqltk is maintained by CipherStash and is a core component of Proxy, our encryption-in-use database proxy.

packages/sqltk-parser is a soft fork of datafusion-sqlparser-rs, and its use is governed by the Apache Software License 2.0.