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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '23bc6f39c5f8f025e5f6cfd4a80634cfc0220611092f1117b267394677fa8a7a' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00013

JSON explain

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