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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21cbefcc3b9787ffcec58f8c2e3f0c424dc50322d1da02cd855551129afa9831' 
  AND token = 'zX5lf9ZEiyQ8hG4nxI2HXRG1AVMauPOXiFpC0VqeE2E=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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