如何检查数据库中的记录是否存在如果存在添加到jtextarea否则留空（netbean）

Question

下面是我的代码，它不起作用。
如果可以，请提供示例代码或编辑我的代码，TY

try {
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:mysql://localhost/timetable", "root", "");
        String sql1 = "select * from tt where day like '%monday%'";
        String sql = "select * from tt where time = 8 ";
        pst = con.prepareStatement(sql);
        pst = con.prepareStatement(sql1);
        rs = pst.executeQuery();
    if (rs.next()) {
        String sC = rs.getString("subjectcode");
        String sN = rs.getString("subjectname");
        String Ln = rs.getString("lecturer");
        monday8to10.setText(sC + newline + "" + sN + newline + "" + Ln);
    } else {
        monday8to10.setText("");
    }
} catch (Exception e) {
    JOptionPane.showMessageDialog(null, e);
}

try {
    Class.forName("com.mysql.jdbc.Driver");
    con = DriverManager.getConnection("jdbc:mysql://localhost/timetable", "root", "");
    String sql1 = "select * from tt where day like '%monday%'";
    String sql = "select * from tt where time = 10 ";
    pst = con.prepareStatement(sql1);
    pst = con.prepareStatement(sql);
    rs = pst.executeQuery();

    while (rs.next()) {
        String sC = rs.getString("subjectcode");
        String sN = rs.getString("subjectname");
        String Ln = rs.getString("lecturer");
        monday10to12.setText(sC + newline + "" + sN + newline + "" + Ln);
    }
} catch (Exception e) {
    JOptionPane.showMessageDialog(null, e);
}

Answer 1

我相信首先，pst.executeQuery() 需要一个参数。您目前根本没有执行任何查询？

pst.executeQuery(sql1);

秒，您需要一次执行 1 个查询：字符串 sql1 = "select * from tt where day like '%monday%'"; 字符串 sql = "select * from tt where time = 10 ";

变成字符串 sql1 = "select * from tt where time = 10 and day like '%monday%'";

例如，我正在回顾我的一些旧数据库代码。

        query = "SELECT m.title, m.year_, m.rt_picture, m.imdb_picture, m.movie_id, u.user_score, u.user_id FROM movie_navigator.movies m, movie_navigator.userratings u WHERE m.movie_id=u.movie_id AND u.movie_id=" + movieId + " LIMIT " + queryPageSize + " OFFSET " + (queryPageSize*pageNumber) + ";";
    try{
        stmt = conn.createStatement();
        results = stmt.executeQuery(query);
        while(results.next()){

如何检查数据库中的记录是否存在如果存在添加到jtextarea否则留空（netbean）

How to check the record in database exist or not if exist add to jtextarea else left blank (netbean)

netbeans-7