检查androidsqlite数据库中的特定列

好的,在遇到更大的问题之前,您应该知道SQLite在ALTERTABLE命令上是有限的,它允许 add 和 rename

所以建议升级:

• 开始移动
• 使用运行表创建 if not exists (我们正在进行升级,因此表可能还不存在,它将失败并删除)
• 将现有列放入列表中 List<String> columns = DBUtils.GetColumns(db, TableName);
• 备份表( ALTER table " + TableName + " RENAME TO 'temp_" + TableName )
• 获取与新列的交集,这次是从升级的表中获取的列( columns.retainAll(DBUtils.GetColumns(db, TableName)); )
• 还原数据( String cols = StringUtils.join(columns, ","); db.execSQL(String.format( "INSERT INTO %s (%s) SELECT %s from temp_%s", TableName, cols, cols, TableName)); )
• 删除备份表( DROP table 'temp_" + TableName )
• 设置事务成功

(这不会处理表降级,如果重命名列,则不会传输现有数据,因为列名不匹配)。

.

public static List<String> GetColumns(SQLiteDatabase db, String tableName) {
    List<String> ar = null;
    Cursor c = null;
    try {
        c = db.rawQuery("select * from " + tableName + " limit 1", null);
        if (c != null) {
            ar = new ArrayList<String>(Arrays.asList(c.getColumnNames()));
        }
    } catch (Exception e) {
        Log.v(tableName, e.getMessage(), e);
        e.printStackTrace();
    } finally {
        if (c != null)
            c.close();
    }
    return ar;
}

public static String join(List<String> list, String delim) {
    StringBuilder buf = new StringBuilder();
    int num = list.size();
    for (int i = 0; i < num; i++) {
        if (i != 0)
            buf.append(delim);
        buf.append((String) list.get(i));
    }
    return buf.toString();
}

找到了解决办法

    try {
            db.execSQL("ALTER TABLE notes" + " ADD COLUMN Week");
        } catch (SQLException e) {
            Log.i("ADD COLUMN Week", "Week already exists");
        }