java - 更新或插入库存程序的代码。扫描结果集时出现问题

Question

我在更新/插入数据到 SQL 表中时遇到问题。下面的代码扫描数据，然后决定是否更新或插入有关表中找到的任何类似数据值的数据。

但是，即使表中有数据，程序也没有执行 rs.next()。

public class newInputSQL {
    Connection conx;
    public newInputSQL(String name, int quantity) {
        try {
            conx = DriverManager.getConnection("jdbc:derby://localhost:1527/InventoryBase", "Serbesius", "N01094L");
            Class.forName("org.apache.derby.jdbc.ClientDriver");
            inputGraphin(name, quantity, conx);
        } catch (SQLException s) {
            System.err.println("SQL error: " + s.toString() + s.getSQLState() + s.getErrorCode());
        } catch (ClassNotFoundException cnfe) {
            System.err.println("Class not found error: " + cnfe.getMessage());
        } finally {
            try {
                conx.close();
            } catch (SQLException ex) {
                System.err.println("Error while cleaning resources. Pass me a proper dustpan" + ex.getMessage());
            }
        }
    }
    public final void inputGraphin(String name, int quantity, Connection conn) throws SQLException {
        String inputName = null;
        Statement st = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
        System.out.println("Inserting data into resultset...");
        ResultSet rs = st.executeQuery("SELECT NAME FROM SERBESIUS.GRAPHINT WHERE NAME ='" + name + "'");
        while (rs.next()) {
            System.out.println("Scanning");
            inputName = rs.getString(1);
            //rs.beforeFirst();
        }
        rs.beforeFirst();
        if (inputName == null) {
            System.out.println("inserting....");
            st.execute("INSERT INTO SERBESIUS.GRAPHINT(NAME, QUANTITY) values('" + name + "', '" + quantity + "')");
        } else if (inputName.equals(name)) {
            System.out.println("Updating.....");
            st.execute("UPDATE SERBESIUS.GRAPHINT SET QUANTITY = '" + quantity + "' WHERE '" + name + "' ");
        }
        // Clean up resources.....
        rs.close();
        st.close();
    }
}

Answer 1

1. 你做的事情比应有的复杂得多。 MySQL已经具备UPSERT/MERGE的功能。

http://dev.mysql.com/doc/refman/5.7/en/insert-on-duplicate.html

连接值 = SQL 注入(inject)。
使用准备好的语句。

https://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html

INSERT INTO SERBESIUS.GRAPHINT(NAME, QUANTITY) values(?,?)
on duplicate key update SET QUANTITY = quantity + ?;

附注

期望别人调试你的代码并不严重。