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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50137da8e640df10b6975632d8ba1bfb6a20bfa0bb7f315db0f233cc19628598' 
  AND token = '/YWZzngMR4nUd0YenskVZfcrnPBhksM1KFFqvzYMscc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00054

JSON explain

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