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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '851b150673d0e42a259288a9486b4fa3603c75e7cb834dc927d503b776198c73' 
  AND token = 'SiEdXqGEmy40JnVn/RQMj0B1FE89MmeZNJkCwXu700g=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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