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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b341d599a428b6b2b60ee0f2a6553ea921e75a747b5db3bd041a7343d968e23c' 
  AND token = 'dARmLZz3+s9MfLMtmvknhSE1PEtiLhWy9qwTY/LBevI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00032

JSON explain

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