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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b84cf8c92d7e4fe879a18e786a552a597c75f0b650c78e63faf02359cd68a404' 
  AND token = 'ms0Bx8xR3vXwWzdAHig+2XE8sXjrj/iqdeMudscZPns=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

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