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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b68f29fa76fbbc4f2ba19492b8bf795a58c396d3449dd969c812c4be2e8c337a' 
  AND token = 'ArqrfAvMWlTZ7HX6SJVQdsgQ38LVwaWiMo1gLgrWr4Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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