`MERGE` statements inside CTEs

[lovasoa]

The following query works in PostgreSQL but returns a parse error in sqlparser:

WITH merged_row AS (
    MERGE INTO users AS cible
    USING (
        SELECT 
            'john.doe'      AS username,
            'password'      AS password,
            'xxxxxxxxxx'    AS uuid,
            TRUE as is_active
    ) AS source
    ON cible.uuid = source.uuid
    WHEN MATCHED THEN
        UPDATE SET 
            username = source.username,
            password = source.password,
            uuid = source.uuid,
            is_active = source.is_active
    WHEN NOT MATCHED THEN
        INSERT (username, password, uuid, is_active)
        VALUES (source.username, source.password, source.uuid, source.is_active)
    RETURNING *
)
SELECT 
    'debug'     AS component,
    COUNT(*)    AS count
FROM merged_row;

The postgres documentation says:

Each auxiliary statement in a WITH clause can be a SELECT, INSERT, UPDATE, DELETE, or MERGE;

-- https://www.postgresql.org/docs/current/queries-with.html

Initially reported in sqlpage/SQLPage#995

[lovasoa]

Here is a more minimal reproduction:

WITH x AS (
  MERGE INTO t USING (VALUES (1)) ON true
    WHEN MATCHED THEN DELETE
  RETURNING *
) SELECT * FROM x