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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b31952cfd4b4a07d97b8b5a592c898cfb0ded1c1013a73a344392795efb40335' 
  AND token = 'CIwUG9ffZPYmYvWmajspzkrYy0elXaa8pXGDtoglj0Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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