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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '3fa78adb311954c2dccd1f0650b97d48472f8e736721efa0ad4d6a2aba9c2a40' 
  AND token = 'EL1tGrJ0/jPPRSQND2/bvi1cQVesv9BLdFRWFU72o/Y=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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