/**
 * SQL Mode 2 — Function Translator
 *
 * String: UPPER, LOWER, TRIM, CONCAT, CONCAT_WS, LENGTH, SUBSTRING
 * Numeric: ROUND, ABS
 * Date: NOW, CURRENT_TIMESTAMP, EXTRACT, DATEDIFF, DATE_ADD, DATE_SUB, DATE_TRUNC, DATE_FORMAT, TIMESTAMPDIFF
 * Conditional: CASE WHEN, COALESCE, NULLIF, CAST, CONVERT
 */
/**
 * Translate a SQL function call to a MongoDB expression.
 * Returns the MongoDB expression object for use in $project or $addFields.
 */
export declare function translateFunction(expr: Record<string, unknown>): Record<string, unknown> | string;
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