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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8b893293946b0f124def271ee80748531e9ef1840c056c78e492d92d5ceef42' 
  AND token = 'PPXlES8y/xb4qwIdcc5OaNpz42sjeuX0dJnXdHwQaWU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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