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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b6f4df072b5c671a111095a5444980214faccaff8c56e38e9b301e4b0124ba98' 
  AND token = 'S3B9aFdz3OcvECHldbziX8uCxZ8n2TucpT2yZ0erArM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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