import { parse, deparse } from 'pgsql-parser';
const sql = `MERGE INTO t AS target
 USING (SELECT 1 AS id) AS source ON target.id = source.id
 WHEN MATCHED THEN UPDATE SET name = 'x'
 WHEN NOT MATCHED THEN INSERT (id, name) VALUES (source.id, 'x')`;
const ast = parse(sql); // succeeds
deparse(ast); // throws: does not handle node type: MergeWhenClause