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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '96fd8f224a8d923a1fd0b07942c9a3c0a5034a20d27537a34851c298d8d9062c' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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