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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '462b5b960bdff355420746712aec127b68f4b2bd8ce17cbd0bf153e64afb0f71' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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