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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21b031c243f730f179aed241e5e322e55279bd4e6b175c54bb8999f6b528173f' 
  AND token = '9ZCTw8CxP+NKEYdNzTvOWYdP5ePybRe8OWDco+8Bdxk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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