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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '255931b20c1b80d9e309844ff82b0dde4aa7488ce2a6c819eff55a9936d3badf' 
  AND token = 'jrKTa+RMZ1ahDQ1TtDBkjnXStZoLVKzP5jyxkdy68v0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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