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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'c878403ef66ada739c0a30b3c6f413755469a2cd8dd16d6f25f282d06d6fe76d' 
  AND token = 'eaPjut3NpzPgWCSBRjtJPj6sQaaQ0jmOyRT7ZFJb1lk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

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