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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a2f50fdca5cb3ace06b31c23323368e9a43b05883f95b378c12f3920aaf57c' 
  AND token = '4HuXsdG28P6lbjvKZVi0a76DwoXMiG2RmYgsY/voCeY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00043

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}