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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c31691561947cfeb57ae5f6d0a90d6906f542e66595ded8661f7f3f7643cab61' 
  AND token = 'U/CvAzUFriPctn67VWivaJGpqza4s30OqPtPFCc5FKU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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