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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6f439bb8ea902c8cfa75bb9ec0fbf6b1459e94f823e385138e5ad8560c2b983a' 
  AND token = 'rNFSFI2xgIjh0cXDYNTm7qoRb+axhQ9xbHIWcHtBv30=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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