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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'c429c91eb72847d70eeeacda988707ee9a7f181c373d5895c30ec19048257507' 
  AND token = '6LlYI1MliZwTRWVnOVZ2qmV85eohs1eM39QaZP/vAjs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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