由网友(心之所向便是光)分享简介：我在找最快的和正确的方法来检查，如果一个记录在数据库中存在：I am looking to the fastest and the correct way to check if a record exists in the database:public boolean Exists(String _id) {C...

我在找最快的和正确的方法来检查，如果一个记录在数据库中存在：

I am looking to the fastest and the correct way to check if a record exists in the database:

public boolean Exists(String _id) {
    Cursor c=db.query(TABLENAME(), new String[] {"1"}, "_ID="+_id, null, null, null, null);
    if (!c.equals(null))
        return c.moveToFirst();
    return false;
}

你看不出什么问题呢？

Do you see any problem with it?

推荐答案

考虑到 MDB 是 SqlLiteDatabase 类

public boolean Exists(String _id) {
   Cursor cursor = mDb.rawQuery("select 1 from yourTable where _id=%s", 
        new String[] { _id })
   boolean exists = (cursor.getCount() > 0);
   cursor.close();
   return exists;
}

在我把你的参数 _id 为字符串，但我认为它应该是一个龙。 选择1 比更快选择COLUMNNAME ，因为这个过程不需要检索的值表的SELECT子句。 您可以将字符串选择1，从... 在静态最终常数甚至更快。

I keep your parameter _id as a String but I think it should be a Long. select 1 is more fast than select columnName because the process doesn't need the retrieve a value from the table in the select clause. you can put the string select 1 from... in a static final constant to be even faster.