Question

当我在Postgres数据库中运行此查询时：

select iid from original where accid=1000 and msg_number=1669;

它总是在Postgres DB中返回一个结果，但是当我在Java中运行它时，它不返回任何结果。

这是original表：

iid: int4
accid: int4
msg_number: int4

这是我的Java代码：

public String getIID(String msgNr) {
    String accid=null;
    try {
        Statement accidStmt = conn.createStatement();
        String accidQuery = "select accid from accounts where name='" + clientname + "'";
        ResultSet accidResult = accidStmt.executeQuery(accidQuery);
        while (accidResult.next())
            accid = accidResult.getString("accid");
        accidResult.close();
        accidStmt.close();
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }

    String iid = null;
    try {
        String iidQuery = "select iid from original where accid=" + accid + " and msg_number=" + msgNr;
        // String iidQuery = "select iid from original where accid=" + Integer.parseInt(accid) + " and msg_number=" + Integer.parseInt(msgNr);
        // String iidQuery = "select iid from original where accid=1000 and msg_number=1669";
        Statement iidStmt = conn.createStatement();
        ResultSet iidResult = iidStmt.executeQuery(iidQuery);
        while (iidResult.next())
            iid = iidResult.getString("iid");
        iidResult.close();
        iidStmt.close();
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }

    return iid;
}

获取accid的第一个查询有效。但是获取iid的第二个查询不起作用，结果总是为0行。正如我的代码所示，我已经尝试将accid转换为Integer，即使我尝试了一个硬值，但此查询并未返回结果。并且它没有进入catch，因为查询执行成功。所以我不知道出了什么问题。

任何帮助都非常感激。

Answer 1

var“accid”是String Object

accid = accidResult.getString("accid");

您应该始终使用预准备语句。请参阅下面的更新功能：

public int getIID(String msgNr) {
    int accid=0;
    try {
        Statement accidStmt = conn.createStatement();
        String accidQuery = "select accid from accounts where name='" + clientname + "'";
        ResultSet accidResult = accidStmt.executeQuery(accidQuery);
        while (accidResult.next())
            accid = accidResult.getInt("accid");
        accidResult.close();
        accidStmt.close();
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }

    int iid = 0;
    try {
        String iidQuery = "select iid from original where accid=? and msg_number=?";
        PreparedStatement pst=conn.prepareStatement(iidQuery);  
        pst.setInt(1,accid);
        pst.setInt(2,Integer.parseInt(msgNr));

        ResultSet iidResult=pst.executeQuery();  
        while (iidResult.next())
            iid = iidResult.getInt("iid");
        iidResult.close();
        iidStmt.close();
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }

    return iid;
}

SQL在Java中没有返回结果，尽管它总是在Postgres中返回结果

1 个答案: