重写 SQLite 语句 SELECT WHERE - Android Eclipse

Posted 2023-04-19

【中文标题】重写 SQLite 语句 SELECT WHERE - Android Eclipse

【英文标题】：Rewrite SQLite statement SELECT WHERE - Android Eclipse

【发布时间】：2016-09-10 18:21:26

【问题描述】：

我编写了一种方法，可以搜索数据库以根据模块查找匹配的讲师。但是，当我运行它时，它会为所有三个保存相同的名称！

方法如下：

public List<tableModules> getStudentsLecturers(String mod1, String mod2, String mod3) 
        List<tableModules> studentModuleLecturer = new ArrayList<tableModules>();       
        // Select All Query to find lecturers depending on modules      
        Log.d("Lecturers", mod1);
        Log.d("Lecturers", mod2);
        Log.d("Lecturers", mod3);
        String selectQuery = "SELECT DISTINCT " + Module_Lecturer + " FROM " + Table2 + " WHERE " + Module_Name + " = \'" + mod1 + "\' OR \'" + mod2 + "\' OR \'" + mod3 + "\'";
        Log.d("1", "1");
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) 
            do                
                tableModules  moduleLecturers = new tableModules();             
                moduleLecturers.modulelecturer = cursor.getString(0);          
                studentModuleLecturer.add(moduleLecturers);         
             while (cursor.moveToNext());
        
        // return lecture list
        return studentModuleLecturer;       
    

然后在 MainActivity.java

中调用

List<tableModules> lecturers = db.getStudentsLecturers(mod1, mod2, mod3);
                if (!lecturers.isEmpty())
                           
                for (tableModules session: lecturers)
                
                    Editor editor = preferences.edit();
                    //Save lecturers to list
                    for (int i=0; i < lecturers.size(); i++) 
                        if (counter == 0)
                                            
                        lecturer1 = session.modulelecturer.toString();
                        editor.putString("lec1", lecturer1);
                        Log.d("Lecs", "1"); 
                        editor.commit();
                        counter++;
                        
                        if (counter == 1)
                                           
                        lecturer2 = session.modulelecturer.toString();
                        editor.putString("lec2", lecturer2);
                        Log.d("Lecs", "2"); 
                        editor.commit();
                        counter++;
                        
                        if (counter == 2)
                           
                        lecturer3 = session.modulelecturer.toString();
                        editor.putString("lec3", lecturer3);
                        Log.d("Lecs", "3"); 
                        editor.commit();
                        counter++;
                        
                        else
                                                       
                            Log.d("Lecs", "ERROR"); 
                        
                       

我知道我正在保存相同的“session.modulelecturer.toString();”每个人，但我不知道如何改变 SQL 方法来为所有三个单独的模块选择所有三个讲师。

【参考方案1】：

尝试替换

" WHERE " + Module_Name + " = \'" + mod1 + "\' OR \'" + mod2 + "\' OR \'" + mod3 + "\'";

与

" WHERE " + Module_Name + " = '" + mod1 + "' OR " + Module_Name + " = '" + mod2 + "' OR " + Module_Name + " = '" + mod3 + "'";

在实践中，你不能说

WHERE ModuleName = 'This' OR 'That'

但你可以说

WHERE ModuleName = 'This' OR ModuleName = 'That'

我知道为每个可能的值重写列名很麻烦，但它在 SQL 中是这样工作的。

---

或者，您可以编写更紧凑的形式：

WHERE ModuleName IN ('This', 'That', '...')

所以你的查询可以变成：

" WHERE " + Module_Name + " IN ('" + mod1 + "', '" + mod2 + "', '" + mod3 + "')";

【讨论】：

出于某种原因，这仍然会为所有三位讲师返回相同的姓名！ :(

那么您为所有 3 个变量传递相同的值。您的查询中有一个错误，这让我眼前一亮，我修复了它。现在在某个地方出现了另一个错误。