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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b55b187e6c5e52d137957a36f55aa657e4103ef5a0f260679bab867cef5bddb9' 
  AND token = '/SJxzGdWBYj2z5ya3jBgupqSeNytwVUot0vx+uAxIIo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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