Contains query analysis implementation for the ClickHouse SQL dialect.

The query analysis is performed on top of a query tree, which is an intermediate representation of SELECT queries. QueryTreeBuilder recursively traverses query AST and creates corresponding query tree nodes. At this stage, the query is in an unresolved state, and all identifiers are represented by IdentifierNode. Later, during analysis, all IdentifierNodes are replaced by ColumnNode, TableNode, or an aliased expression. There should be no IdentifierNode in the resolved query tree.

This folder contains definitions for all Query Tree components and utility functions for them.

The Resolve/ folder contains functionality responsible for the identifier resolution and type inference. QueryAnalyzer performs identifier resolution, constant folding and substitutes all the used in the query aliases and CTEs. Some parts of the query may still be unresolved after that, e.g., some table functions arguments.

The Passes/ folder contains implementations of query tree level optimizations. All of them are implementations of the IQueryTreePass interface. In most cases, they use InDepthQueryTreeVisitorWithContext to traverse the query and modify some query tree nodes. Please note that InDepthQueryTreeVisitor, compared to InDepthQueryTreeVisitorWithContext, doesn't know about unresolved parts of the query tree and doesn't keep track of the correct subquery Context. It traverses the whole subtree starting from the root node passed to it; thus, it should be used only when you are sure it's safe.

The tests/ folder contains unit tests for some parts of the query tree infrastructure.