删除哪些字段具有指定值的记录

Question

我正在尝试删除具有我指定值的字段的记录：

public static void delete(String firstName, String lastName, int age)
{
    try 
    {
        Statement myStmt = connection.createStatement();
        String sql = "delete from students where firstName='" + firstName + "', lastName='" + lastName + "', age='" + age + "'";
        myStmt.executeUpdate(sql);
    } 
    catch (SQLException e)
    {e.printStackTrace();}
}

代码不起作用。我绝对肯定它的问题。请帮我做正确的sql。如何在表中找到我指定的字段值的记录？

这是我遇到的错误：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'where firstName='deleted', lastName='deleted', age='10'' at line 1
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.Util.getInstance(Util.java:408)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:943)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2527)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2680)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2486)
    at com.mysql.jdbc.StatementImpl.executeUpdateInternal(StatementImpl.java:1552)
    at com.mysql.jdbc.StatementImpl.executeLargeUpdate(StatementImpl.java:2607)
    at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1480)
    at Driver.delete(Driver.java:76)
    at Driver.main(Driver.java:18)

Answer 1

为了避免所有这些语法错误甚至 SQL 注入，您必须使用 PreparedStatement，因此您可以使用：

String query = "delete from students where firstName=? and lastName=? and age=?";
try (PreparedStatement delete = connection.prepareStatement(query)) {

    delete.setString(1, firstName);
    delete.setString(2, lastName);
    delete.setInt(3, age);//<-----------(1)

    delete.executeUpdate();
}

• (1) 我不确定年龄是 int 还是 varchar，所以如果年龄是字符串，则必须改用 setString。

---

您真正的问题是您必须在where 中使用and、or 而不是,

 where firstName='" + firstName + "', lastName='" + lastName + "', age='" + age + "'";
//----------------------------------^----------------------------^

Answer 2

你的SQL不正确，应该是：

String sql = "DELETE FROM students WHERE firstName='" + firstName + "' AND lastName='" + lastName + "' AND age='" + age + "'";

您只能使用关键字分隔 WHERE 子句中的条件，例如 AND 或 OR 逗号在 SQL 查询的那部分是无效的分隔符。