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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '255dfeeb5e2ca70a1df0c633f52e9a93abb93eaa471755d69c04c727da928a08' 
  AND token = 'g0g5OBpJq+u+0zydQNEanK7olnHKIK8qltrgGM0wXII=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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