/**
 * AST visitor to qualify unqualified column references in JOIN ON clauses.
 *
 * Stock Drizzle renders an aliased SQL field of a subquery or CTE by its bare
 * alias, so `eq(table.col, sq.col)` becomes `"table"."col" = "col"`, which
 * DuckDB rejects as ambiguous. Selects built by this driver already qualify
 * those fields (see exposeSubqueryFields), so this mostly covers raw SQL. The unqualified side is given to the newly joined
 * source unless the qualified side already is that source. When that cannot
 * be decided, the reference is left as it is.
 *
 * Other unqualified references to the same name in SELECT, WHERE, GROUP BY,
 * HAVING and ORDER BY get the qualifier chosen in the ON clause. Names that
 * were given different qualifiers, and USING columns, are left unqualified.
 *
 * Performance optimizations:
 * - Early exit when no unqualified columns found in ON clause
 * - Skip processing if all columns are already qualified
 * - Minimal tree traversal when possible
 */
import type { AST } from 'node-sql-parser';
export declare function qualifyJoinColumns(ast: AST | AST[]): boolean;