如何在Android的Sqlite数据库中使用where子句执行SELECT查询？

Question

如何在android中使用where子句获取SQLite数据库的唯一列。 我想从数据库中获取数值，然后将其与其他数值进行比较，我该怎么办？

Answer 1

有多个步骤来实现这一点。

1. 通过扩展SQLiteOpenHelper类创建一个类。提及数据库名称，表名，所有列名以及创建和删除语句。

AndroidOpenDbHelper：

public class AndroidOpenDbHelper extends SQLiteOpenHelper implements BaseColumns{ 

public static final String DB_NAME = "Test_DB"; 
public static final int DB_VERSION = 2; 
public static final String TABLE_NAME_TEST = "Test_Table"; 
public static final String COLUMN_NAME_LOC = "Location"; 
public static final String COLUMN_NAME = "Name"; 
public static final String TEXT_TYPE = " TEXT"; 
public static final String COMMA_SEP = ","; 
public static final String SQL_CREATE_TABLE = "CREATE TABLE "+AndroidOpenDbHelper.TABLE_NAME_TEST+" ("+AndroidOpenDbHelper._ID+" INTEGER PRIMARY KEY"+COMMA_SEP+AndroidOpenDbHelper.COLUMN_NAME_LOC+TEXT_TYPE+COMMA_SEP+AndroidOpenDbHelper.COLUMN_NAME+TEXT_TYPE+")"; 
public static final String SQL_DROP_TABLE = "DROP TABLE IF EXISTS "+AndroidOpenDbHelper.TABLE_NAME_TEST; 

public AndroidOpenDbHelper(Context context) 
{ 
    super(context,DB_NAME,null,DB_VERSION); 
} 

public void onCreate(SQLiteDatabase db) 
{ 
    db.execSQL(SQL_CREATE_TABLE); 
} 

public void onUpgrade(SQLiteDatabase db, int OldVersion, int NewVersion) 
{ 
    db.execSQL(SQL_DROP_TABLE); 
    onCreate(db); 
} 

public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) 
{ 
    onUpgrade(db, oldVersion, newVersion); 
} 
} 

1. 在你MainActivity，调用此类初始化数据库和表。

   try 
   { 
       AndroidOpenDbHelper openDbHelperObj = new AndroidOpenDbHelper(this); 
       SQLiteDatabase sqLiteDatabase = openDbHelperObj.getWritableDatabase(); 
       ContentValues contentValues = new ContentValues(); 
   
       contentValues.put(AndroidOpenDbHelper.COLUMN_NAME_LOC,Location); 
       contentValues.put(AndroidOpenDbHelper.COLUMN_NAME,Name); 
   
       long affectedRowId = sqLiteDatabase.insert(AndroidOpenDbHelper.TABLE_NAME_TEST,null,contentValues); 
   
       sqLiteDatabase.close(); 
   
   }catch(Exception err) 
   { 
       err.printStackTrace(); 
   } 
   

2. 最后将此添加到要检索和显示数据的活动中。

   public static final String SQL_SELECT_QUERY = "SELECT * FROM "+AndroidOpenDbHelper.TABLE_NAME_TEST+" WHERE "+AndroidOpenDbHelper.COLUMN_NAME_LOC = +'Location'; 
   
   AndroidOpenDbHelper queryDbHelperObj = new AndroidOpenDbHelper(this); 
       SQLiteDatabase sqLiteDatabase = queryDbHelperObj.getReadableDatabase(); 
       Cursor cursor = sqLiteDatabase.rawQuery(SQL_SELECT_QUERY,null); 
   
       if(cursor != null) 
       { 
        if(cursor.moveToFirst()) 
        { 
         do 
         { 
          String Location= cursor.getString(cursor.getColumnIndex("Location")); 
          String DestinationDB = cursor.getString(cursor.getColumnIndex("Name")); 
   
         }while(cursor.moveToNext()); 
        } 
       } 
   

可能有一些问题与查询的语法，所以我建议你改正和执行。

希望这会有所帮助！

开始=>