Question

使用oracle数据库，我需要检查我的'users'表中的用户是否被禁止。如果用户的“禁止”栏的值为“1”，则禁止用户，如果不是，则禁止“0”。

我在这里有以下工作代码：

public boolean banUser(String username)
    {//TODO check if user is banned already
        try 
        {
            pstmnt = conn.prepareStatement("UPDATE users SET banned = 1 WHERE username = ?");
            pstmnt.setString(1, username);
            pstmnt.execute();
            logger.info("Banned User : " + username);
            return true;
        } catch ( SQLException e ) { e.getMessage(); }
        return false;
    }

我不确定如何在准备好的声明之上执行if语句。有什么想法吗？

Answer 1

从以下位置更改您的更新声明：

conn.prepareStatement("UPDATE users SET banned = 1 WHERE username = ?");

为：

conn.prepareStatement("UPDATE users SET banned = 1 WHERE username = ? and banned = 0");

使用executeUpdate()代替execute()执行。区别在于executeUpdate返回受更新影响的行数，因此如果用户已被禁止，则无需执行SQL语句来检索。

//...
pstmnt = conn.prepareStatement("UPDATE users SET banned = 1 WHERE username = ? and banned = 0");
pstmnt.setString(1, username);
int affectedRows = pstmnt.executeUpdate();
boolean wasUserBanned = affectedRows > 0;
//...

Answer 2

使用此查询，并将结果存储在ResultSet

中

SELECT * FROM users WHERE username = ? AND banned = 1

这将返回所有具有特定用户名的被禁用户。

pstmnt = conn.prepareStatement("SELECT * FROM users WHERE username = ? AND banned = 1");
pstmnt.setString(1, username);
ResultSet rs = pstmnt.executeQuery();
if(rs.next()) {
    //The user is banned
} else {
    //The user is not banned
}

如果您需要方法版本：

public boolean isUserBanned(String user) throws SQLException {
    pstmnt = conn.prepareStatement("SELECT * FROM users WHERE username = ? AND banned = 1");
    pstmnt.setString(1, username);
    ResultSet rs = pstmnt.executeQuery();
    return rs.next();
}

Answer 3

这是我对@ BackSlash版本的变体，假设username具有UNIQUE约束：

pstmnt = conn.prepareStatement(
    "SELECT COUNT(*) FROM users WHERE username = ? AND banned = 1");
pstmnt.setString(1, username);
ResultSet rs = pstmnt.executeQuery();  // Always returns exactly one row.
rs.next();
return rs.getBoolean(1);               // Converts 0, 1 to false, true.

您可以让数据库使用

完成更多工作

CREATE VIEW BANNED_USERS AS
    SELECT username FROM USERS
    WHERE banned = 1;

Answer 4

更新后运行选择：

    pstmnt = conn.prepareStatement("SELECT banned FROM users WHERE username = ?");
    Resultset rs = pstmnt.execute();
    pstmnt.setString(1, username);
    int isBanned = 0;
    while(rs.next()) {
        isBanned = rs.getInt(1);
    }
    if(isBanned == 1) {
        System.out.println("User is banned")
    }

Answer 5

重用您的代码:(假设用户已存在）

public boolean isUserBanned(String username)
    {//TODO check if user is banned already
        try 
        {
            pstmnt = conn.prepareStatement("select username WHERE username = ? and banned = 1");
            pstmnt.setString(1, username);
            Resultset rs = pstmnt.executeQuery();
            //logger.info("Banned User : " + username);
            return rs.next();
        } catch ( SQLException e ) { e.getMessage(); }
        return false;
    }

检查数据库中的用户是否被禁止JDBC

5 个答案: