Question

这是使用GUI获取用户输入并在MySQL中创建关系表的Web应用程序的一部分。问题是为什么没有创建表？使用调试器，问题出在

期间

st.executeUpdate(tableCreation.toString());

所以我试着这样做

String[] Tables = {
        tableCreation.toString()
};

for (int i = 0; i < Tables.length; ++i) {
     st.executeUpdate(Tables[i]);
}

但它也不起作用。我之所以这样做的原因是因为在使用静态数组String时创建了表

static String[] Tables = {
    "create table STATE (" +
    "ABBREVIATION char(2) not null, " +
    "NAME varchar(32) not null, " +
    "ENTERED_UNION date null, " +
    "CAPITAL varchar(32) not null, " +
    "REGION varchar(16) not null, " +
    "AREA int not null, " +
    "FLOWER varchar(32) null, " +
    "BIRD varchar(32) null)"
};

当我使用静态表时，它可以工作。所以我想知道出了什么问题？

public String createButton1_action() {

    StringBuilder tableCreation = new StringBuilder();

    tableCreation.append("create table ").append(tableTF.getValue()).append(" (");

    StringBuilder primaryKey = new StringBuilder();

    for (int i = 0; i < column; i++) {
        // first get() returns the gridPanel, second get() returns the components within the panel
        TextField tempTF = (TextField) gridPanels.get(i).getChildren().get(1);
        // the table name from textfield
        tableCreation.append(tempTF.getValue()).append(" ");

        // the data type
        DropDown tempDP = (DropDown) gridPanels.get(i).getChildren().get(3);
        tableCreation.append(tempDP.getValue()).append(" ");
        // char/varchar amount
        if (tempDP.getValue().equals("CHAR") || tempDP.getValue().equals("VARCHAR")) {
            TextField charTF = (TextField) gridPanels.get(i).getChildren().get(4);
            tableCreation.append(charTF.getValue()).append(" ");
        }

        // primary key
        tempDP = (DropDown) gridPanels.get(i).getChildren().get(6);
        addPK(tempTF, tempDP, primaryKey);

        // nullable?
        tempDP = (DropDown) gridPanels.get(i).getChildren().get(8);
        tableCreation.append(tempDP.getValue());

        tableCreation.append(", ");
    }

    tableCreation.append("PRIMARY KEY (").append(primaryKey).append(")");
    tableCreation.append(")");

    String[] Tables = {
        tableCreation.toString()
    };

    try {
        // Get a connection from the connection factory
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/testDB", "root", "onfigii");

        // Create a Statement object so we can submit SQL statements to the driver
        Statement st = con.createStatement();

        // Submit the statement (Doesn't work too. It worked with a static table)
        for (int i = 0; i < Tables.length; ++i) {
            st.executeUpdate(Tables[i]);
        }

        // Why doesn't this work?
        st.executeUpdate(tableCreation.toString());

        // Close the statement
        st.close();

        // Close the connection
        con.close();

    } catch (SQLException ex) {
        Logger.getLogger(CreatePage.class.getName()).log(Level.SEVERE, null, ex);
    }


    tableTF.setText(null);
    for (int i = 0; i < column; i++) {
        TextField tempTF = (TextField) gridPanels.get(i).getChildren().get(1);
        tempTF.setValue(null);
    }

    getApplicationBean1().refreshDataProvider();
    return null;
}

谢谢。

Answer 1

它应该是：

create table a
(b DOUBLE default null,
c CHAR (10) default NULL,
d DATE NOT NULL,
e VARCHAR (20) default NULL,
PRIMARY KEY (b, d)
);

你能显示失败的sql示例吗？

Answer 2

问题在于逻辑。而不是

tableCreation.append(charTF.getValue()).append(" ");

应该是

tableCreation.append("(").append(charTF.getValue()).append(")").append(" ");

回答我自己的问题，

没有错

st.executeUpdate(tableCreation.toString());

它首先不起作用的原因是因为创建表的语法开头是错误的。因此，静态字符串表工作，而逻辑创建的字符串不起作用。

Java JDBC executeUpdate用法

2 个答案: