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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '9d7394382bf1d9f72a660e5c35a1cf1e0a77aa2420061daec4762d1269ea1603' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00015

JSON explain

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