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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51c28562158c1861119488f60df0f664830d5b35caa622351a6032d59ab1ca41' 
  AND token = 'x5lYvtlLgNtwqeH3USr0fFgTXyiBuDT5HPyDYWiJsFk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00059

JSON explain

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