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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a878b744c4ad352f2899d2f481c91962fc258548c1bbe9400a338769daf7b7a8' 
  AND token = '+L5zEl9VdTWbShXCOv7NV9TrVGmGY+nhin2sndowbRw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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