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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a7521329ee30e0ee33ba1019773f297b45a969aca23467ff1e0ad1a2da54a54c' 
  AND token = 'rU1TpJlv2UGcwOnVkzhFl/T98pGHUbftKc1KSmPRN70=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00037

JSON explain

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