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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '15981aa77c085753e12f097def5c8fe3a7857bd515110b5ffd53c42e5c12d0c9' 
  AND token = '+WblT5xzCIfSEMwmoZGZ2WV0xkUa8JS10n7RgRSdtko=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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