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SELECT 
  role_system, 
  role_user, 
  role_assistant 
FROM 
  cscart_pw_chat_gpt_sessions_chat 
WHERE 
  session = '16d638e5945032fbc8df0a0a23f7d6' 
order by 
  id desc 
LIMIT 
  5

Query time 0.00026

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_pw_chat_gpt_sessions_chat	index		PRIMARY	4		5	Using where