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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '9f51af1c4e88472c9e647125e00bb42f9a773c97e1b42a1b2eb1823ec988ed04' 
  AND token = 'zUMOVm4ZCEzEPcofA7TKH2yfejDIRHBofsnxm3nHk9E=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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