delete só pode lidar com uma tabela por vez, então você precisaria de três instruções:DELETE FROM upklist
WHERE session_id = (SELECT session_id
FROM usession
WHERE delete_session_id IS NULL
AND user_id = (SELECT user_id
FROM users
WHERE REGEXP_LIKE(USER_NAME,
'awpeople', 'i')));
DELETE FROM projshar
WHERE session_id = (SELECT session_id
FROM usession
WHERE delete_session_id IS NULL
AND user_id = (SELECT user_id
FROM users
WHERE REGEXP_LIKE(USER_NAME,
'awpeople', 'i')));
DELETE FROM usession
WHERE session_id = (SELECT session_id
FROM usession
WHERE delete_session_id IS NULL
AND user_id = (SELECT user_id
FROM users
WHERE REGEXP_LIKE(USER_NAME,
'awpeople', 'i')));
Observe que, como a consulta interna depende de
usersession , você deve excluir dele último . 
