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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '303d308da2f4422a176f7f5975f0d81e25a1bdedb3ec84936cb1aac29ddba0af' 
  AND token = 'DAx++7pIZ1lhoAn4J+SmJ9qMYmAUImoo6OZVcuOJv3c=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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