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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e3a8988f2b3f0c20e202fe09ddb4f5afaf9514aabb4aeb7f324290a717cea7d7' 
  AND token = 'UQBx9h4ofwVjn0X+QsIRePdrftRDhOEGSLyJJ35JQBk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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