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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '5a557552dfb7fea84855fda89492e6d97c3123879917f31c62b08422eae6a136' 
  AND token = '9v4jEaEP+4vvyuY+qaogJKbU2B69NOpcgSavUaacFF4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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