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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'c79a423943984a2d9999e5a32261cf55f34c5b5bcac0f770f5a3301a8f4358a6' 
  AND token = 'wDHFiHgtHWXbiMWXakWa8mfu3BSrv00Z0BPaNs+ijaE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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