java - 插入之前检查数据库中是否有重复项

Question

在插入表之前，我需要检查数据库中的记录是否已存在。我有两张表，一张用于插入数据，一张是引用主表的日志表。在这个日志表中，我有 ID、date_import 和 file_import。所以我想检查 file_import 是否已经存在。

这是我的临时代码:

    //DATE
        DateFormat dateF = new SimpleDateFormat("dd.MM.yyyy");
        Date date = new Date();
//DATE        

//DB INIT
        String URL = "jdbc:mysql://192.168.1.128:3306";
        Connection con = (Connection) DriverManager.getConnection(URL,user,pass);
        Statement stmt = (Statement) con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
        Statement stmt1 = (Statement) con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
        String mySQL_log = ("CREATE TABLE IF NOT EXISTS dbtest.T_AJPES_TR_LOG"
            + "(ID INT unsigned PRIMARY KEY AUTO_INCREMENT, Date_import VARCHAR(45),"
            + "File_import VARCHAR(75)) ENGINE = INNODB");
        String mySQL_new_table = ("CREATE TABLE IF NOT EXISTS dbtest.T_AJPES_TR "
            + "(row_count INT PRIMARY KEY AUTO_INCREMENT,"
            + "rn CHAR(15),sSpre CHAR(5),reg CHAR(5),eno VARCHAR(10),davcna VARCHAR(15),Ime VARCHAR(75),"
            + "Priimek VARCHAR(75),ID_LOG INT unsigned,"
            + "CONSTRAINT FOREIGN KEY(ID_LOG) references T_AJPES_TR_LOG(ID) ON DELETE CASCADE ON UPDATE CASCADE) ENGINE = INNODB");

        stmt1.executeUpdate(mySQL_log);
        ResultSet uprs1 = stmt1.executeQuery("SELECT * FROM dbtest.T_AJPES_TR_LOG");
        stmt.executeUpdate(mySQL_new_table);
        ResultSet uprs = stmt.executeQuery("SELECT * FROM dbtest.T_AJPES_TR");
//SELECT INIT

//READ FILE        
        File folder = new File(readFolder);
        String[] fileName = folder.list();

        for (;k<fileName.length;k++) {
            name = fileName[k];
            if (name.contains(".xml")) {
            FileInputStream fstream = new FileInputStream(readFolder + name);
            DataInputStream in = new DataInputStream(fstream);
            BufferedReader br = new BufferedReader(new InputStreamReader(in));
//READ FILE
            uprs.next();
            file_exists = uprs1.getString("File_import");

            if (!file_exists.equals(name)) {
                uprs1.afterLast();
                uprs1.moveToInsertRow();
                uprs1.updateString("Date_import",dateF.format(date));
                uprs1.updateString("File_import",name);
                uprs1.insertRow();
                i=0;

Answer 1

我可能误解了你的问题，但如果你发送

SELECT * FROM dbtest.T_AJPES_TR_LOG WHERE file_import='MyFileName.xml';

对于数据库，您将得到一个空结果集(= 实际文件名是新的)或一个包含 1..n 个条目的结果集(= 文件名已知并且已被记录 1..n 次)。

<小时/>

将其放在引号中，正如 Knubo 所说:

String query = String.format(
    "SELECT * FROM dbtest.T_AJPES_TR_LOG WHERE File_import='%s'", name);
uprs1 = stmt1.executeQuery(query);