Some key points of Android App using SQLite database

SQLiteDatabase db = openOrCreateDatabase(File file, , Factory factor);

(sql)     //Execute any SQL statement(table, nullColumnHack, value)   //(increase)(table, whereClause, whereArgs)  //(delete)(table, values, whereClause, whereArgs) //(change)（table,columns,whereClause,whereArgs,groupBy,having,orderBy) //(check)(sql, selectionArgs)  //You can use SQL statements to query directly

( int offset)  //The cursor moves up or down the specified number of rows, positive number down, negative number up, negative number up()    //Move to the first row and return the boolean value()
()
(int postion)  //Move to the specified row and return the boolean value()  //Move to the previous line();       //Whether to point to the first item();       //Whether to point to the last one();  //Whether to point to the first item();   //Whether to point to the last one(int columnIndex); //Specify whether the column is empty (column cardinality is 0)();     //Is the cursor closed();    //Total number of data items();  //Return the number of rows pointed to by the current cursor(String columnName); //Return the column index value corresponding to a column name(int columnIndex);         //Return the value of the specified column in the current row

protected void onCreate(Bundle savedInstanceState) {
  (savedInstanceState);
  setContentView(.activity_main);
  //Each program has its own database and does not interfere with each other  //Create a database and open it. This method returns a SQLiteDadabase object (if there is no, create it, and if there is, open it directly)  //The name of this database is, so that it is named to facilitate third-party software to open after exporting to the computer. The second parameter is a constant. This example means that other private databases cannot be accessed  SQLiteDatabase db = openOrCreateDatabase("", MODE_PRIVATE, null);
  //Create a table usertb, and the primary key name is recommended to write it as _id, 1 primary key, 3 columns, plus _id, a total of 4 columns.   ("create table if not exists usertb(_id integer primary key autoincrement, name text not null, age integer not null, sex text not null)");
  //Add 3 pieces of data into this table usertb, 3 columns, and 3 corresponding values   ("insert into usertb(name, age, sex) values('Jack','18','male')");
   ("insert into usertb(name, age, sex) values('Hellen','19','female')");
   ("insert into usertb(name, age, sex) values('Mike','20','male')");

  //Query data. The first parameter is still a statement. The query method specifies how to find query conditions. The second parameter is the query conditions. All data is query by default.  //The return value here is Cursor, which is a class of the management set obtained after querying data. It can be understood as a list (cursor interface)  Cursor c = ("select * from usertb", null);
   if (c!= null){                    //If the data can be found     ();                //If the data has not been processed, this line can be omitted, the first line of the default cursor is the first line.     while(()){          //Only one data can be queried at a time to determine whether the next line can be queried (key point: after each cursor reaches one line, the following statement prints the data in that line in sequence, loops, and prints the next line of data)        ("info", " "+ (("_id")));       //The first field int type needs to be converted to String type before printing with Log (find the integer type data with field angle marked 0 in this data)       ("info", (("name")));      //The second field is text type       ("info", " "+(("age")));
       ("info", (("sex")));
       ("info", "~~~~~~~~");                          //Test how much data is printed in a loop     }
     ();                                  //After query, the cursor must be released   }
   ();    
}

put(String key，Xxx);
getAsXxx（String Key）;

 SQLiteDatabase db = openOrCreateDatabase("", MODE_PRIVATE, null);
  ("create table if not exists usertb(_id integer primary key autoincrement, name text not null, age integer not null, sex integer not null) ");

  //Before executing the addition and modification methods, first create a ContentValues ​​object in the insert method, then store data on this object, and insert values ​​into it after saving.  ContentValues values = new ContentValues(); 
  //increase  ("name", "Zhang San");
  ("age",18);
  ("sex","male");
  ("usertb", null, values);  //The return value of the insert method is a long, indicating the line number of the newly added record  ();    //Before inserting the next data, you need to clear the values ​​and then store the new data in the values  ("name", "Li Si");
  ("age",19);
  ("sex","male");
  ("usertb", null, values);  
  ();
  ("name", "Wang Wu");
  ("age",20);
  ("sex","male");
  ("usertb", null, values);  
  ();
  //Change (change the gender with id greater than female  ("sex", "female");
  ("usertb", values, "_id >?", new String[]{"2"});
  //Delete (Delete the person with three in his name)  ("uesrtb", "name like ?", new String [] {"%three%"});
  //Check (Query usertb table, all rows are bad, and the data with _id > 0 are checked, and the data found are sorted by name)  Cursor c = ("usertb", null, "_id > ?", new String[]{"0"}, null, null, "name");

  ();

  //Close the current database  ();
  //Delete the database (note that it is not the table name)  deleteDatabase("");

SQLiteDatabase db = ();
SQLiteDatabase db = ();

public class DBOpenHelper extends SQLiteOpenHelper{    
  public DBOpenHelper(Context context, String name) {
    super(context, name, null, 1);
  }
  public DBOpenHelper(Context context, String name, CursorFactory factory,int version) {
    super(context, name, factory, version);
  }

  @Override//Called when creating a database for the first time. Generally, the operation of building a database and building a table can be used.  public void onCreate(SQLiteDatabase db) {
    ("create table if not exists stutb(_id integer primary key autoincrement,name text not null,sex text not null,age integer not null)");
    ("insert into stutb(name,sex,age)values('Zhang San','female',18)");
  }

  @Override//It will be automatically executed when the database version changes  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

  }
}

DBOpenHelper helper =new DBOpenHelper(, "");
SQLiteDatabase db = ();