1、 getWritableDatabase()和getReadableDatabase()区别
两个方法都会返回SQLiteDatabase实例。其中getReadableDatabase()是先读取数据库，如果此时磁盘空间满就会打开失败，当打开失败时候，就会继续尝试以只读的方式打开数据库。如果磁盘空间够用就会返回一个可读写的数据库对象。
而使用getWritableDatabase()方式打开数据库，如果磁盘满了，数据库就只读不能写了，此时打开数据库就会报错。
2、query和rawQuery的区别
Cursor cursor = db.rawQuery("select name from *** where id=?", new String[]{"1"});
Cursor cursor = db.query("***", new String[]{"name"}, "id=?", new String[]{"1"}, null, null, null);
上面是两个分别是query和rawQuery的查询语句，主要区别是rawQuery是直接使用SQL语句进行查询的，也就是第一个参数字符串，在字符串内的“？”会被后面的String[]数组逐一对换掉；而query函数是Android自己封装的查询API：它的API文档如下：
public Cursor query (String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
Query the given table, returning a Cursor over the result set.
table
The table name to compile the query against.
columns
A list of which columns to return. Passing null will return all columns, which is discouraged to prevent reading data from storage that isn't going to be used.
selection
A filter declaring which rows to return, formatted as an SQL WHERE clause (excluding the WHERE itself). Passing null will return all rows for the given table.
selectionArgs
You may include ?s in selection, which will be replaced by the values from selectionArgs, in order that they appear in the selection. The values will be bound as Strings.
groupBy
A filter declaring how to group rows, formatted as an SQL GROUP BY clause (excluding the GROUP BY itself). Passing null will cause the rows to not be grouped.
having
A filter declare which row groups to include in the cursor, if row grouping is being used, formatted as an SQL HAVING clause (excluding the HAVING itself). Passing null will cause all row groups to be included, and is required when row grouping is not being used.
orderBy
How to order the rows, formatted as an SQL ORDER BY clause (excluding the ORDER BY itself). Passing null will use the default sort order, which may be unordered.
Returns
•A Cursor object, which is positioned before the first entry. Note that Cursors are not synchronized, see the documentation for more details.
而后者query对比前者来讲就有一个好处，前者rawQuery你在写入SQL语句的时候，有可能写错了或者写漏了什么单词拼写错误的时候他会出错，而后者相对来讲出错的机率就比较小
