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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '51e9fcb93d1208a71dd091de5d659bda2ae02910c4c2576afac95fec32dee53e' 
  AND token = '7J9wAxHIc7py9B4cXnOEKoXpEnNUQrskdDCjbzDQwNo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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