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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '503c2cf3ebf13c4e087aefbccabe93d30fe02087c207eff6a286672b10a61aa6' 
  AND token = 'B9WQUkca+ORB1dImbILx9IqMMUWHo+S52eiQqt2DrK8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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