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SELECT 
  1 
FROM 
  cscart_ec_print_temp_designs 
WHERE 
  session_id = 'P2EM-M0S8-1CM7-8E54-1MHB-4L7P-YZPP-10VH' 
  AND product_id = 29 
  AND expires_at > 1770301511 
  AND confirmed = 'Y' 
LIMIT 
  1

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}