How to get column value from sqlite cursor?

问题

I am trying to get column value from a cursor, this column is generated at run time by calculations inside the query, I am getting a null value of this column, I am able to get a value of all other columns which exists in SQLite table.

I execute the same query on SQLite editor, it also shows the value of generated column in result set.

Why this giving null value when I am retrieving it from cursor?

回答1:

Very Simple you can get it by either of following way

String id = cursor.getString( cursor.getColumnIndex("id") ); // id is column name in db

or

String id = cursor.getString( cursor.getColumnIndex(0)); // id is first column in db

回答2:

Cursor column names are case sensitive, make sure you match the case specified in the db or column alias name

回答3:

1. If you don't know column index in select query the follow this,

   Define constant for all fields of table so it is easy to get field name you don't need to verify its spell

   create Database Costant class with name "DBConstant.java" and define table fields

   public static final String ID = "id";

   Then get value from cursor,

   cursor.getString(cursor.getColumnIndex(DBConstant.ID));

   cursor.getColumnIndex(field name); it returns field column index in you select statement cursor.getString(column index). it returns value which is on that column

2. If you know column index in your select query,

   cursor.getString(0);

回答4:

If you want to get string value

String id = cursor.getString( cursor.getColumnIndex("name") ); // id is column name in db
or

String id = cursor.getString( cursor.getColumnIndex(0)); 

If you want to get Integer value

String id = cursor.getInt( cursor.getColumnIndex("id") ); // id is column name in db
or

String id = cursor.getInt( cursor.getColumnIndex(0)); 

回答5:

In Android Studio 3.4.1 (I use Kotlin but it does not make any difference here), I've discovered a very odd behaviour.

For instance:

Cursor c = db.rawQuery("Select IDH, ID, NOME, CONTEUDO from CalcHome 
           Inner Join Calcs using(id)", null)

The column names was registered in a rigid way, independent of case of field names in Select. The array component c.columnNames[0] is Idh not IDH

So

int a = c.getInt(c.getColumnIndex("IDH")) // gives a runtime error.

But

int a = c.getInt(c.getColumnIndex("Idh")) // works!

来源：https://stackoverflow.com/questions/9412040/how-to-get-column-value-from-sqlite-cursor