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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a0447466b168e1f7a3c221fd7614a52799f1d76ffd8a9d1d41f5d14585f515e3' 
  AND token = 'jZXLPiQua2ARUM4+aso9lObGmEhlMZ2W9f4tmpvsbHk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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