用 java 更新數據庫中的產品數量

Question

我正在建立一個超市系統，我想在用戶銷售該產品時更新庫存數量，我寫了這個 function `

    public String setqty(String bar){
    String qty = "SELECT SUM(QTY) FROM sales_product WHERE barcode = '"+bar+"'";
    int quantity = Integer.parseInt(qty);
    String sql = "update product set Qty = Qty - " + quantity + " where Barcode = " + bar;
    String str = (String) db.database.getTableData(sql).items[0][0];
    
    return str;
}` 

但是當我嘗試運行它時，我得到了這些錯誤

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "SELECT SUM(QTY) FROM sales_product WHERE barcode= '12345'"

我該如何解決該錯誤

Answer 1

根據您的代碼，您正在使用 Integer.parseInt 解析 sql 字符串。 您需要在兩者之間調用數據庫

String qtySQL = "SELECT SUM(QTY) FROM sales_product WHERE barcode = '"+bar+"'";
String qty = (String) db.database.getTableData(qtySQL).items[0][0] //Now holding the value of sum(qty), if I got the syntax right
int quantity = Integer.parseInt(qty);
String sql = "update product set Qty = Qty - " + quantity + " where Barcode = " + bar;
String str = (String) db.database.getTableData(sql).items[0][0];

return str;